A population of the world's most aggressive mosquito species was almost completely wiped out by an experiment on two islands in the southern Chinese province of Guangdong, according to a study published.
The experiment successfully reduced the female Asian Tiger Mosquito population — the main source of bites and disease spread — by up to 94%, reducing the number of reported human bites by 97%.
One of the Chinese study's researchers, Xi Zhiyong, a professor at Michigan State University, has been a longtime pioneer in this field of study. Running a mosquito factory in southern China, he previously attempted to use sterilized male mosquitoes to mate with unaltered females which developed normally. In the new study, published by the International Journal of Science, Xi and his colleagues attempted to cut mosquito numbers even further by limiting both males and females' ability to reproduce. The results were so successful that they nearly killed the entire female mosquito population on the two islands.
It isn't the first attempt by researchers to reduce mosquito populations across the world. In 2018, scientists from the Imperial College of London used gene-editing tools to make female mosquitoes sterile, while males developed normally and continued spreading the genetic mutation (突变).Experts said the Asian Tiger Mosquitoes are particularly hard to kill using traditional population control methods, such as pesticides (杀虫剂) and removing stagnant (不流动的) water where the insects lay their eggs.
Mosquitoes create grave threats to human health beyond just bites. The World Health Organization (WHO) has described the insects as "one of the deadliest animals in the world," due to their ability to rapidly spread deadly diseases such as dengue fever and malaria. There is currently no effective vaccine or treatment for most mosquito-spread diseases, leaving controlling the insects' populations one of the most effective control methods, according to the International Journal of Science. “A new tool like what's being described in this paper is very much needed” said Stephen Dobson, a professor of medical insectology at University of Kentucky.
1.What does the underlined word "unaltered" in paragraph 3 refer to?
A.Unchanged. B.Undivided.
C.Unadopted. D.Unfinished.
2.Why do mosquito populations have to be controlled?
A.Mosquitoes cause genetic changes in humans.
B.Mosquitoes spread some deadliest diseases.
C.Mosquitoes limit people's ability to reproduce.
D.Mosquitoes make traditional vaccines ineffective.
3.What has been the most successful way of reducing mosquito numbers?
A.Editing genes in female mosquitoes.
B.Sterilizing male mosquitoes before mating.
C.Limiting both genders' reproduction ability.
D.Using pesticides and removing stagnant water.
4.What can we learn from Stephen Dobson's words?
A.The things described in this paper are not practical.
B.A better way of mosquito control is yet to be found.
C.Xi Zhiyong' s method has proven to be very effective.
D.A new tool is needed in order to improve Xi's research.
高三英语阅读理解中等难度题
A population of the world's most aggressive mosquito species was almost completely wiped out by an experiment on two islands in the southern Chinese province of Guangdong, according to a study published.
The experiment successfully reduced the female Asian Tiger Mosquito population — the main source of bites and disease spread — by up to 94%, reducing the number of reported human bites by 97%.
One of the Chinese study's researchers, Xi Zhiyong, a professor at Michigan State University, has been a longtime pioneer in this field of study. Running a mosquito factory in southern China, he previously attempted to use sterilized male mosquitoes to mate with unaltered females which developed normally. In the new study, published by the International Journal of Science, Xi and his colleagues attempted to cut mosquito numbers even further by limiting both males and females' ability to reproduce. The results were so successful that they nearly killed the entire female mosquito population on the two islands.
It isn't the first attempt by researchers to reduce mosquito populations across the world. In 2018, scientists from the Imperial College of London used gene-editing tools to make female mosquitoes sterile, while males developed normally and continued spreading the genetic mutation (突变).Experts said the Asian Tiger Mosquitoes are particularly hard to kill using traditional population control methods, such as pesticides (杀虫剂) and removing stagnant (不流动的) water where the insects lay their eggs.
Mosquitoes create grave threats to human health beyond just bites. The World Health Organization (WHO) has described the insects as "one of the deadliest animals in the world," due to their ability to rapidly spread deadly diseases such as dengue fever and malaria. There is currently no effective vaccine or treatment for most mosquito-spread diseases, leaving controlling the insects' populations one of the most effective control methods, according to the International Journal of Science. “A new tool like what's being described in this paper is very much needed” said Stephen Dobson, a professor of medical insectology at University of Kentucky.
1.What does the underlined word "unaltered" in paragraph 3 refer to?
A.Unchanged. B.Undivided.
C.Unadopted. D.Unfinished.
2.Why do mosquito populations have to be controlled?
A.Mosquitoes cause genetic changes in humans.
B.Mosquitoes spread some deadliest diseases.
C.Mosquitoes limit people's ability to reproduce.
D.Mosquitoes make traditional vaccines ineffective.
3.What has been the most successful way of reducing mosquito numbers?
A.Editing genes in female mosquitoes.
B.Sterilizing male mosquitoes before mating.
C.Limiting both genders' reproduction ability.
D.Using pesticides and removing stagnant water.
4.What can we learn from Stephen Dobson's words?
A.The things described in this paper are not practical.
B.A better way of mosquito control is yet to be found.
C.Xi Zhiyong' s method has proven to be very effective.
D.A new tool is needed in order to improve Xi's research.
高三英语阅读理解中等难度题查看答案及解析
Hong Kong is one of the most densely populated (人口密集的)cities in the world, but with night skies around 1,000 times brighter than globally accepted levels, it gains a bad reputation for its light pollution.
A study by Hong Kong University found that brightness levels in the southern Chinese city's popular shopping district of Tsim Sha Tsui were 1,200 times greater than the international dark sky standard.
The crowded city of 7 million residents(居民), full or residential high-rises, towering office blocks and neon(霓虹灯) advertisements, has no laws to control outdoor lightning.
The result is that light pollution is thought to be much worse than in other large cities, including London, Sydney, Tokyo and Shanghai.
“In Hong Kong , you can’t go anywhere outdoor in the evening without your eyes being blinded by this really disturbing outdoor lightning,” the light pollution survey’s head Jason Pum told AFP.
“The fact that we have all this light in the sky means energy is wasted,” he said, adding that too much artificial lightning also affects nightly wildlife.
Research has suggested that light pollution can cause a number of harmful health effects in humans, including sleeplessness and headaches and can also interrupt body clocks and hormones(荷尔蒙).
The university survey, the result of five million measurements taken from points across the city, was released just days before the start of the annual Earth Hour event, organized by the World Wildlife Fund.
People around the world will be encouraged to turn off the lights for an hour on Saturday night to raise awareness of climate change. Last year, a number of Hong Kong’s major buildings along Victoria Harbour went dark to mark Earth Hour.
“Anyway, we should do our best to reduce the amount of lightning and adjust it for the benefit of the environment.”
1.If you walk out at night in Hong Kong, you can see all those things except ______.
A. neon advertisements B. residential buildings
C. a dark sky with twinkling stars D. high office blocks
2..which of the following statements about too much lightning is NOT true?
A. Too much lightning means a waste of energy.
B. It can make the sky and the city more beautiful.
C. It may have a bad effect on nightly wildlife.
D. It can lead to some health problems.
3..We can know from the passage that__________
A. light pollution in Hong Kong is among world’s worst.
B. light pollution is the biggest problem in Hong Kong.
C. Earth Hour is simply organized to reduce pollution.
D. light pollution is the primary causes of sleeplessness.
4..what will the author probably discuss after the last paragraph?
A. Bad effects of light pollution
B. Causes of light pollution
C. Worries about light pollution
D. Ways to reduce light pollution
高三英语阅读理解中等难度题查看答案及解析
Over the past five decades mosquito populations in parts of the U.S. have skyrocketed by a factor of 10-a situation with worrying implications for the spread of diseases. And some places are apparently more easily affected than others. A new study in the Journal of Medical Entomology found that in Baltimore, low-income neighborhoods bear the biggest burden: they have not only more mosquitoes but also larger ones, which often survive longer. The problem most likely is rooted in the fact that Baltimore has nearly 17,000 abandoned buildings, which are concentrated in economically disadvantaged areas and serve as convenient mosquito-breeding zones.
Compared with prosperous blocks, low-income blocks have more abandoned buildings and are more heavily littered with thrown-away containers that collect standing water. And water that pools in abandoned buildings is protected by shade-which helps mosquitoes grow larger. Some cities take efforts to plant trees in low-income blocks but may actually worsen the problem: trees and bushes not only shade outdoor breeding(繁殖) pools but also shed leaves into the water and feed the mosquito larvae(幼虫), helping them grow bigger. Worse still, climate change could worsen the disease landscape by broadening habitats and lengthening the time every summer that mosquitoes can breed and survive.
Cities may, then, need to focus more mosquito-control efforts on these areas. Urban health departments typically educate homeowners about the importance of emptying water out of outdoor containers. But nobody empties those in or around abandoned buildings. “It is something that is fairly difficult for a city to address because it’s really expensive to go into private belongings and clean them up,” says Dina Fonseca, a molecular ecologist at Rutgers University. Yet if these belongings become breeding grounds not only for annoying mosquitoes but also for dangerous diseases, officials’ concepts may need to change.
1.What does the phrase “a factor of 10” in Paragraph 1 refer to?
A.A major cause. B.A high rate.
C.A big concern. D.A special situation.
2.Why is the spread of diseases relatively more serious in poor neighborhoods in Baltimore?
A.Because people there lack the awareness of waste sorting.
B.Because people there pay little attention to water protection.
C.Because more thrown-away containers are collected for reuse there.
D.Because more abandoned buildings serve as habitats for mosquitoes there.
3.Which of the following solutions is well-intentioned but may result in opposite effects?
A.Planting more trees. B.Changing officials’ ideas.
C.Emptying water containers. D.Cleaning abandoned buildings.
4.What is the author’s purpose in writing the text?
A.To complain about the poor housing. B.To offer some treatments for diseases.
C.To appeal for mosquito-control efforts. D.To introduce a new species of mosquitoes.
高三英语阅读理解中等难度题查看答案及解析
The sound of a mosquito can mean trouble in many parts of the world. The bite of the mosquito can be deadly. The insects carry serious diseases like malaria (疟疾). It is estimated that almost 630,000 people died from malaria and malariarelated causes in 2012, and most of these cases were in African countries.
In the United States, a group of California scientists are working to develop a more effective and less costly substance (物质) to protect people from mosquitoes. The researchers are investigating the sense of smell in mosquitoes. They found the insects use the same receptor for identifying carbon dioxide in human breath as they do for the smell of our skin. Anandasankar Ray, who is leading the investigation, says scientists tested more than a million chemical compounds (化合物) until they found a substance called Ethyl Pyruvate. He says Ethyl Pyruvate makes the mosquitoes' receptors inactive. “When we apply Ethyl Pyruvate to a human arm and offer it to hungry mosquitoes in a cage, very few of the mosquitoes are attracted to the human arm because only a few of them are able to smell it out,” said Ray.
Genevieve Tauxe, a member of the research team, says it was not easy to find the neurons (神经元) of noble cells that recognize both the smell of human breath and skin. “With the device used to examine the mosquito, we are able to insert a very small electrode (电极) into the part of the mosquito's nose, where its smelling neurons are and where the smell is happening,” said Tauxe.
Anandasankar Ray says a product based on Ethyl Pyruvate may cost less to produce than DEFT, the most effective chemical treatment now in use. He says DEFT is too costly for most people who live in areas affected by malaria.
“Perhaps by finding smells that can attack other target receptors, we will be able to improve upon DEFT and finally have the next generation of insect behaviour control products,” said Ray.
1.The underlined word in the second paragraph probably means ________.
A. a substance that protects people from mosquitoes
B. a piece of equipment that sends signals
C. a device that reacts to light
D. a sense organ that reacts to changes
2.According to the passage, Ethyl Pyruvate can ________.
A. kill the mosquitoes' smelling neurons
B. cause the mosquitoes to lose their senses of smell
C. result in the inactiveness of the mosquitoes' receptors
D. make the mosquitoes uninterested in human breath and skin smell
3.Which of the following would be the best title for the passage?
A. Ethyl Pyruvate—an Insect Behaviour Control Product
B. Malaria—a Serious Disease Causing 630,000 Deaths
C. Scientists Find a New Substance to Fight Mosquitoes
D. A New Generation of DEET Has Been Developed to Kill Mosquitoes
4.This passage most probably appears in ________.
A. a textbook of medical schools
B. a collection of doctors' essays
C. the column of newspaper ads
D. the health column of a magazine
高三英语阅读理解中等难度题查看答案及解析
The sound of a mosquito can mean trouble in many parts of the world. The bite of the mosquito can be deadly. The insects carry serious diseases like malaria. It is estimated that almost 630,000 people died from malaria and malaria-related causes in 2012, and most of these cases were in African countries.
In the United States, a group of California scientists is working to develop a more effective and less costly substance(物质)to protect people from mosquitoes. The researchers are investigating the sense of smell in mosquitoes. They found the insects use the same receptor(感受器)for identifying carbon dioxide in human breath as they do for the smell of our skin. Anandasankar Ray, who is leading the investigation, says scientists tested more than a million chemical compounds(化合物)until they found a substance called Ethyl pyruvate. He says Ethyl pyruvate makes the mosquitoes' receptor inactive. ”When we apply Ethyl pyruvate to a human arm and offer it to hungry mosquitoes in a cage, very few of the mosquitoes are attracted to the human arm because only a few of them are able to smell it out,” said Ray.
Genevieve Tauxe, a member of the research team, says it was not easy to find the neurons (神经元)of nose cells that recognise both the smell of human breath and skin. "With the device used to examine mosquitoes, we are able to insert a very small electrode(电极)into the part of the mosquitoes' nose, where its smelling neurons are and where the smell is happening," said Tauxe.
Anandasankar Ray says a product based on Ethyl pyruvate may cost less to produce than DEFT，the most effective chemical treatment now in use. He says DEFT is too costly for most people who live in areas affected by malaria.
“Perhaps by finding smells that can attack other target receptors, we will be able to improve upon DEFT and finally have the next generation of insect behavior control products," said Ray.
1.The best title for the passage is most probably _______________________________.
A. Scientists Find New Substance to Fight Mosquitoes
B. A New Generation of DEET Has Been Developed to Kill Mosquitoes
C. Malaria一a Serious Disease Causing 630,000 Deaths
D. Ethyl Pyruvate一an Insect Behavior Control Product
2.According to the passage, Ethyl Pyruvate can_______________________________.
A. kill the mosquitoes' smelling neurons
B. cause the mosquitoes to lose their sense of smell
C. result in the inactiveness of the mosquitoes' receptor
D. make the mosquitoes uninterested in human breath and skin smell
3.Through the passage, the writer aims to_______________________________.
A. inform readers of the new development in fighting mosquitoes
B. praise the achievements made in the battle against malaria
C. introduce a cheaper product in fighting mosquitoes
D. tell the differences between Ethyl Pyruvate and DEET
4.This passage most probably appears in_______________________________.
A. the column of newspaper ads
B. the health column of a magazine
C. a textbook of medical schools
D. a collection of doctors' essays
高三英语阅读理解困难题查看答案及解析
How does an ecosystem(生态系统) work? What makes the populations of different species the way they are? Why are there so many flies and so few wolves? To find an answer, scientists have built mathematical models of food webs, noting who eats whom and how much each one eats.
With such models, scientists have found out some key principles operating in food webs. Most food webs, for instance, consist of many weak links rather than a few strong ones. When a predator(掠食动物) always eats huge numbers of a single prey(猎物), the two species are strongly linked; when a predator lives on various species, they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species, it can survive the extinction(灭绝) of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare, the switch allows the original prey to recover. The weak links may thus keep species from driving one another to extinction.
Mathematical models have also revealed that food webs may be unstable, where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s, scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species—including species they did not directly attack.
And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean, we fished for top predators such as cod on an industrial scale, while on land, we killed off large predators such as wolves. These actions have greatly affected the ecological balance.
Scientists have built an early-warning system based on mathematical models. Ideally, the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key, scientists say, because once ecosystems pass their tipping point(临界点), it is remarkably difficult for them to return.
1.What have scientists discovered with the help of mathematical models of food webs?
A.The living habits of species in food webs.
B.The rules governing food webs of the ecosystems.
C.The approaches to studying the species in the ecosystems.
D.The differences between weak and strong links in food webs.
2.A strong link is found between two species when a predator ________.
A.has a wide food choice
B.can easily find new prey
C.sticks to one prey species
D.can quickly move to another place
3.What will happen if the populations of top predators in a food web greatly decline?
A.The prey species they directly attack will die out.
B.The species they indirectly attack will turn into top predators.
C.The living environment of other species will remain unchanged.
D.The populations of other species will experience unexpected changes.
4.What conclusion can be drawn from the examples in Paragraph 4?
A.Uncontrolled human activities greatly upset ecosystems.
B.Rapid economic development threatens animal habitats.
C.Species of commercial value dominate other species.
D.Industrial activities help keep food webs stable.
5.How does an early-warning system help us maintain the ecological balance?
A.By getting illegal practices under control.
B.By stopping us from killing large predators.
C.By bringing the broken-down ecosystems back to normal.
D.By signaling the urgent need for taking preventive action.
高三英语阅读理解困难题查看答案及解析
How does an ecosystem(生态系统)work？What makes the populations of different species the way they are？Why are there so many flies and so few wolves？To find an answer，scientists have built mathematical models of food webs，noting who eats whom and how much each one eats.
With such models，scientists have found out some key principles operating in food webs. Most food webs，for instance，consist of many weak links rather than a few strong ones. When a predator(掠食动物)always eats huge numbers of a single prey(猎物)，the two species are strongly linked；when a predator lives on various species，they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species，it can survive the extinction(灭绝)of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare，the switch allows the original prey to recover. The weak links may thus keep species from driving one another to extinction.
Mathematical models have also revealed that food webs may be unstable，where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s，scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species---including species they did not directly attack.
And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean，we fished for top predators such as cod on an industrial scale，while on land，we killed off large predators such as wolves. These actions have greatly affected the ecological balance.
Scientists have built an early-warning system based on mathematical models. Ideally，the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key，which scientists says because once ecosystems pass their tipping point(临界点)，it is remarkably difficult for them to return.
1.What have scientists discovered with the help of mathematical models of food webs？
A.The living habits of species in food webs.
B.The rules governing food webs of the ecosystems.
C.The approaches to studying the species in the ecosystems.
D.The differences between weak and strong links in food webs.
2.A strong link is found between two species when a predator______
A.has a wide food choice B.can easily find new prey
C.sticks to one prey species D.can quickly move to another place
3.What conclusion can be drawn from the examples in Paragraph 4？
A.Uncontrolled human activities greatly upset ecosystems.
B.Rapid economic development threatens animal habitats.
C.Species of commercial value dominate other species.
D.Industrial activities help keep food webs stable.
4.How does an early-warning system help us maintain the ecological balance？
A.By getting illegal practices under control.
B.By stopping us from killing large predators.
C.By bringing the broken-down ecosystems back to normal.
D.By signaling the urgent need for taking preventive action.
高三英语阅读理解困难题查看答案及解析
The sight of a mosquito can mean trouble to people in many parts of the world. The bite of the mosquito can be deadly. The insects carry serious diseases like malaria (疟疾). It is estimated that almost 630,000 people died from malaria and malariarelated causes in 2012, and most of these cases were in African countries.
In the United States, a group of California scientists are working to develop a more effective and less costly substance (物质) to protect people from mosquitoes. The researchers are investigating the sense of smell in mosquitoes. They found the insects use the same receptor for identifying carbon dioxide in human breath as they do for the smell of our skin. Anandasankar Ray, who is leading the investigation, says scientists tested more than a million chemical compounds (化合物) until they found a substance called Ethyl Pyruvate. He says Ethyl Pyruvate makes the mosquitoes' receptors inactive. “When we apply Ethyl Pyruvate to a human arm and offer it to hungry mosquitoes in a cage, very few of the mosquitoes are attracted to the human arm because only a few of them are able to smell it out,” said Ray.
Genevieve Tauxe, a member of the research team, says it was not easy to find the neurons (神经元) of noble cells that recognize both the smell of human breath and skin. “With the device used to examine the mosquito, we are able to insert a very small electrode (电极) into the part of the mosquito's nose, where its smelling neurons are and where the smell is happening,” said Tauxe.
Anandasankar Ray says a product based on Ethyl Pyruvate may cost less to produce than DEFT, the most effective chemical treatment now in use. He says DEFT is too costly for most people who live in areas affected by malaria.
“Perhaps by finding smells that can attack other target receptors, we will be able to improve upon DEFT and finally have the next generation of insect behaviour control products,” said Ray.ytytzygx.
1.The underlined word in the second paragraph probably means ________.
A. a substance that protects people from mosquitoes
B. a sense organ that reacts to changes
C. a device that reacts to light
D. a piece of equipment that sends signals
2.According to the passage, Ethyl Pyruvate can ________.
A. kill the mosquitoes' smelling neurons
B. cause the mosquitoes to lose their senses of smell
C. result in the inactiveness of the mosquitoes' receptors
D. make the mosquitoes uninterested in human breath and skin smell
3.This passage most probably appears in ________.
A. a textbook of medical schools
B. a collection of doctors' essays
C. the column of newspaper ads
D. the health column of a magazine
4.Which of the following would be the best title for the passage?
A. Ethyl Pyruvate—an Insect Behaviour Control Product
B. Malaria—a Serious Disease Causing 630,000 Deaths
C. Scientists Find a New Substance to Fight Mosquitoes
D. A New Generation of DEET Has Been Developed to Kill Mosquitoes
高三英语阅读理解中等难度题查看答案及解析
China’s Scariest Outdoor Attractions
As the world’s most populous nation with the world’s second-biggest economy, China is finding new and increasingly adventurous ways to attract and entertain tourists.
Fuxi Mountain, Henan
Guinness World Records receives 2,000 applications from China a year -- more than any other country. And the latest potential record-breaker is the 3,000-ton glass-and-steel skywalk at Fuxi Mountain in Henan province, central China. Visitors who dare walk on this U-shaped bridge can look straight through the glass to the valley floor about 360 meters below. The new bridge extends 30 meters beyond the cliff edge, trumping other U-shaped wonders such as Arizona’s Grand Canyon Skywalk over the epic US gorge.
Shilinxia, Beijing
32.8 meters over the edge of a 396-meter valley, the Shilinxia Viewing Platform stretches a whole 11 meters farther than Grand Canyon Skywalk. It’s constructed with titanium alloy, the material used in airplanes and space shuttles, so it can apparently hold a maximum load of 150 tons and 2,000 people. It’s a hefty 1.5-hour hike from the valley floor to the platform. Or taking the cable car up is an option.
East Taihang, Hebei
The glass walkway at the East Taihang Scenic Area in northern Hebei Province gained popularity last year when video emerged showing a terrified tour guide falling to his hands and knees as the glass apparently started cracking under his weight. Shattered glass fragments were placed underneath solid panels to make the walkway look and sound as though it’s cracking when trodden upon. While the unique walkway of Taihang Mountain is therefore safe to traverse, tourists were quick to point out that at 1,180 meters above sea level, it could still induce thrill.
1.To arrive at the platform in Shilinxia, you can .
A.walk B.take cars
C.take cable cars D.both A and C
2.Which of the following attractions is likely to break the world record?
A.Grand Canyon Skywalk
B.Walkway at East Taihang
C.U-shaped bridge at Fuxi Mountain
D.Viewing platform at Shilinxia
3.What do we know about the tourist attractions mentioned in the passage?
A.Travelers won’t feel frightened since the glass walkway at Taihang isn’t cracking.
B.Both attractions at Fuxi Mountain and Shilinxia extend farther than Grand Canyon skywalk.
C.The viewing platform at Shilinxia can hold more than 2000 people.
D.The material used in airplanes is applied to the glass walkway at East Taihang.
高三英语阅读理解中等难度题查看答案及解析
India has the second _______ population in the world.
| A．larger | B．most | C．smallest | D．largest |
高三英语单项填空简单题查看答案及解析