Fever, coughing, sore throat… most of us at one time or another have had these symptoms. What causes them? In fact, many diseases are caused by viruses, including some deadly ones like AIDS, SARS and COVID-19, also known as the novel coronavirus pneumonia, outbreak in China.
What are viruses? How can viruses cause so much trouble? Viruses are very small particles (颗粒) which are about one millionth of an inch long. Unlike human cells or bacteria, viruses aren’t living organisms- they can't reproduce on their own. Instead, they invade the cells of living organisms to reproduce, spread and take over.
Virus can infect every living thing- from plants and animal down to the smallest bacteria. For this reason, they are always a potential danger to humans. Viruses lie around our environment all of the time, waiting for a host cell to come along. They can enter our bodies by the nose, mouth, eyes or breaks in the skin. Once inside, they try to find a host cell to infect. For example, HIV, which causes AIDS, attacks the T-cells of the immune system.
But the basic question is, where did viruses first come from? Until now, no clear explanation for their origin exists. "Tracing the origins of viruses is difficult, "Ed Rybicki, a scientist at the university of Cape Town in South Africa, told Scientific American, "because viruses don' t leave fossils and because of the tricks they use to make copies of themselves within the cells they've invaded.”
However, there are three main theories to explain the origin of viruses. First, viruses started as dependent organisms, then became parasites(寄生者)。Second, viruses evolved from pieces of DNA or RNA that "escaped" .from larger organisms. Third, viruses co-evolved with their host cells, which means they existed alongside these cells.
For the time being, these are only theories. The technology and evidence we have today cannot be used to test these theories and identify the most reasonable explanation. Continuing studies may provide us with clearer answers or future studies may find that the answer is even more mysterious than it now appears.
1.What can we learn about viruses from the text?
A.Viruses are really small living organisms.
B.Viruses have nothing to do with the common cold.
C.Viruses can't reproduce unless they find a host cell.
D.Viruses enter our bodies mainly through our mouths, noses and hair.
2.Why are viruses always a potential danger to humans?
A.TH most infect all the living things around us.
B.They prefer evolving with the cells in our body.
C.They can copy human's DNA and evolve successfully.
D.They can enter our body far more easily than other living things.
3.Which of the following might explain the origin of viruses?
A.They evolved from the DNA of animals.
B.They evolved along with their host cells.
C.They evolved from the fossils of large organisms.
D.They evolved from parasites to independent organisms.
4.What can we conclude from the last paragraph?
A.The author is confident about future virus research.
B.Viruses will become more like bacteria as they evolve.
C.Viruses live longer in human host cells than in animals.
D.It may take a long time to understand the origin of viruses.
高二英语阅读理解中等难度题
Fever, coughing, sore throat… most of us at one time or another have had these symptoms. What causes them? In fact, many diseases are caused by viruses, including some deadly ones like AIDS, SARS and COVID-19, also known as the novel coronavirus pneumonia, outbreak in China.
What are viruses? How can viruses cause so much trouble? Viruses are very small particles (颗粒) which are about one millionth of an inch long. Unlike human cells or bacteria, viruses aren’t living organisms- they can't reproduce on their own. Instead, they invade the cells of living organisms to reproduce, spread and take over.
Virus can infect every living thing- from plants and animal down to the smallest bacteria. For this reason, they are always a potential danger to humans. Viruses lie around our environment all of the time, waiting for a host cell to come along. They can enter our bodies by the nose, mouth, eyes or breaks in the skin. Once inside, they try to find a host cell to infect. For example, HIV, which causes AIDS, attacks the T-cells of the immune system.
But the basic question is, where did viruses first come from? Until now, no clear explanation for their origin exists. "Tracing the origins of viruses is difficult, "Ed Rybicki, a scientist at the university of Cape Town in South Africa, told Scientific American, "because viruses don' t leave fossils and because of the tricks they use to make copies of themselves within the cells they've invaded.”
However, there are three main theories to explain the origin of viruses. First, viruses started as dependent organisms, then became parasites(寄生者)。Second, viruses evolved from pieces of DNA or RNA that "escaped" .from larger organisms. Third, viruses co-evolved with their host cells, which means they existed alongside these cells.
For the time being, these are only theories. The technology and evidence we have today cannot be used to test these theories and identify the most reasonable explanation. Continuing studies may provide us with clearer answers or future studies may find that the answer is even more mysterious than it now appears.
1.What can we learn about viruses from the text?
A.Viruses are really small living organisms.
B.Viruses have nothing to do with the common cold.
C.Viruses can't reproduce unless they find a host cell.
D.Viruses enter our bodies mainly through our mouths, noses and hair.
2.Why are viruses always a potential danger to humans?
A.TH most infect all the living things around us.
B.They prefer evolving with the cells in our body.
C.They can copy human's DNA and evolve successfully.
D.They can enter our body far more easily than other living things.
3.Which of the following might explain the origin of viruses?
A.They evolved from the DNA of animals.
B.They evolved along with their host cells.
C.They evolved from the fossils of large organisms.
D.They evolved from parasites to independent organisms.
4.What can we conclude from the last paragraph?
A.The author is confident about future virus research.
B.Viruses will become more like bacteria as they evolve.
C.Viruses live longer in human host cells than in animals.
D.It may take a long time to understand the origin of viruses.
高二英语阅读理解中等难度题查看答案及解析
Tiredness, coughing, a runny nose and a sore throat—among all sicknesses there is probably none more common than the flu (流感), which we all get now and then. However, bird flu is a completely different story.
In 2003, the H5N1 bird flu swept across 15 countries, including China, with sufferers reporting chest pain, difficulty breathing, fever and severe coughing. More than 600 people were infected, and about 60 percent died. Now, another type of bird flu hit Shanghai and three neighboring provinces, and this time the virus is called H7N9. By the afternoon of April 11, the new virus had taken nine lives out of 35 infected, according to Xinhua News Agency.
The “H” and “N” in the virus’ name refer to two kinds of proteins (蛋白质) on the surface of the virus. Any change of the numbers of the two proteins indicates a new mutation(变异). Most of the mutations only affect birds, such as chickens and pigeons, and don’t normally spread to humans. But once they do, the results can be disastrous.
“Any time an animal influenza virus crosses to humans, it is a cause for concern, ” Malik Peiris, virologist (病毒学家) at the University of Hong Kong, told Nature magazine. Take the SARS epidemic (传染病) in 2003 as an example. The virus behind the disease is thought to have jumped to humans from animals. The virus was a complete “stranger” to human bodies, which hadn’t developed an immunity (免疫力) against it.
But there is something more about the new H7N9 bird flu. Unlike the H5N1 bird flu, which causes severe sickness in birds, the H7N9 has been evolving under the radar(悄悄地) since it travels between birds without causing noticeable illness. That makes it difficult to keep track of the disease.
The good news is that there’s so far no sign that the virus is spreading from person to person. But since there is no vaccine (疫苗) for the disease yet, the World Health Organization recommends that you wash your hands after meeting with sick people and before and after you eat or prepare food, and they also suggest avoiding contact with birds or their eggs.
1.Which of the following statements is TRUE according to the text?
A. The H5N1 bird flu turned out to have something to do with the SARS epidemic.
B. More than 600 people across the world died from the H5N1 bird flu in 2003.
C. Most of the mutations of the proteins in the bird flu virus are harmful to both birds and humans.
D. The name, H7N9 bird flu, shows that there have been new mutations of the proteins in the virus.
2.With the example of the SARS epidemic in Paragraph 5, the author intends to .
A. introduce where the SARS virus came from
B. inform us of the harmful effects of the SARS epidemic ten years ago
C. show the horrible effects an animal influenza virus can have once it spreads to humans
D. compare the differences between the SARS epidemic and the H7N9 bird flu
3.What makes the H7N9 bird flu more frightening than the H5N1 bird flu according to the text?
A. It can cause severe sickness in birds.
B. It can spread from person to person.
C. It affects a greater number of birds.
D. It doesn’t sicken birds and thus can spread unnoticed.
4.What are people advised to do to protect themselves against the H7N9 bird flu?
a. To get vaccinated for the disease. b. To keep away from birds and their eggs.
c. To stop eating chickens and ducks. d. To avoid meeting with sick people.
e. To wash hands thoroughly and regularly.
A. a, b B. c, d C. b, e D. a, e
高二英语阅读理解中等难度题查看答案及解析
Tiredness, coughing, a runny nose and a sore throat—among all sicknesses there is probably none more common than the flu (流感), which we all get now and then. However, bird flu is a completely different story.
In 2003, the H5N1 bird flu swept across 15 countries, including China, with sufferers reporting chest pain, difficulty breathing, fever and severe coughing. More than 600 people were infected, and about 60 percent died. Now, another type of bird flu hit Shanghai and three neighboring provinces, and this time the virus is called H7N9. By the afternoon of April 11, the new virus had taken nine lives out of 35 infected, according to Xinhua News Agency.
The “H” and “N” in the virus’ name refer to two kinds of proteins (蛋白质) on the surface of the virus. Any change of the numbers of the two proteins indicates a new mutation(变异). Most of the mutations only affect birds, such as chickens and pigeons, and don’t normally spread to humans. But once they do, the results can be disastrous.
“Any time an animal influenza virus crosses to humans, it is a cause for concern, ” Malik Peiris, virologist (病毒学家) at the University of Hong Kong, told Nature magazine. Take the SARS epidemic (传染病) in 2003 as an example. The virus behind the disease is thought to have jumped to humans from animals. The virus was a complete “stranger” to human bodies, which hadn’t developed an immunity (免疫力) against it.
But there is something more about the new H7N9 bird flu. Unlike the H5N1 bird flu, which causes severe sickness in birds, the H7N9 has been evolving under the radar(悄悄地) since it travels between birds without causing noticeable illness. That makes it difficult to keep track of the disease.
The good news is that there’s so far no sign that the virus is spreading from person to person. But since there is no vaccine (疫苗) for the disease yet, the World Health Organization recommends that you wash your hands after meeting with sick people and before and after you eat or prepare food, and they also suggest avoiding contact with birds or their eggs.
1.Which of the following statements is TRUE according to the text?
A. The H5N1 bird flu turned out to have something to do with the SARS epidemic.
B. More than 600 people across the world died from the H5N1 bird flu in 2003.
C. Most of the mutations of the proteins in the bird flu virus are harmful to both birds and humans.
D. The name, H7N9 bird flu, shows that there have been new mutations of the proteins in the virus.
2.With the example of the SARS epidemic in Paragraph 5, the author intends to .
A. introduce where the SARS virus came from
B. inform us of the harmful effects of the SARS epidemic ten years ago
C. show the horrible effects an animal influenza virus can have once it spreads to humans
D. compare the differences between the SARS epidemic and the H7N9 bird flu
3.What makes the H7N9 bird flu more frightening than the H5N1 bird flu according to the text?
A. It can cause severe sickness in birds.
B. It can spread from person to person.
C. It affects a greater number of birds.
D. It doesn’t sicken birds and thus can spread unnoticed.
4.What are people advised to do to protect themselves against the H7N9 bird flu?
a. To get vaccinated for the disease. b. To keep away from birds and their eggs.
c. To stop eating chickens and ducks. d. To avoid meeting with sick people.
e. To wash hands thoroughly and regularly.
A. a, b B. c, d C. b, e D. a, e
高二英语阅读理解中等难度题查看答案及解析
阅读理解E
Do you have a sore throat, a running nose and a headache? Do you keep coughing and sneezing? If you do, the chances are that you have a cold or perhaps flu---but which one? Although both colds and flu are caused by viruses, they are very different illnesses.
Colds, which usually last about a week, affect the nose most. They commonly cause a running nose and sneezing. Sometimes, they cause a headache, a cough and slightly aching muscles.
Flu is a much more serious illness and is caused by different groups of viruses. People with flu usually get all the symptoms(症状) described above. However, they also get a high fever, a dry cough and much worse aching. Fever is one of the characteristic symptoms of the flu for all ages. The symptoms also last much longer. Sometimes they don’t disappear for at least two weeks.
Flu can be a deadly disease. The elderly(年长的), who are weaker and less healthy than most younger people, can die from flu. This is one reason why old people are advised to have a flu injection(预防针) before the start of winter when flu is most common. This injection is inexpensive and definitely（明显地）worth it.
If you have a cold or flu, you must always deal with used tissues(手巾纸) carefully. Don’t leave dirty tissues on your desk or on the floor. Someone else has to pick these up and viruses could be passed on. And finally, remember to cover your nose and mouth when you sneeze! You don’t want to see the small drops of liquids blown(喷) out of your nose and mouth when you sneeze, do you? Disgusting(令人作呕), eh? Now you can understand why it’s a good idea to cover your nose and mouth when you sneeze!
【小题１】 In paragraph 4, we learn that ________.
A. flu injection can cause death B. most old people die from flu
C. flu can kill old people easily D. flu is most common in summer
【小题１】 Dealing with used tissues properly(正确地) is important because ________.
A. it helps keep your classroom tidy B. it prevents the spread of colds and flu
C. people hate picking up dirty tissues D. picking up lots of tissues is hard work
【小题１】 Which of the following statements is TRUE according to the passage?
A. Both colds and flu last the same time.
B. Both colds and flu can be prevented by injection.
C. Both colds and flu are caused by the same viruses.
D. Both colds and flu have an aching symptom.
【小题１】Which is probably the best title for the passage?
A. Colds and Flu B. The Different Symptoms of a Cold and Flu
C. Prevention Is Better Than Cure
D. Cover Your Nose and Mouth When Sneezing
高二英语阅读理解简单题查看答案及解析
The most common disease in the world is the cold. It often starts with a sore throat（咽部疼痛）. You sneeze (打喷嚏) and your nose runs. You usually have a headache, too. Often you have a cough later. It's not a serious disease, but you can feel quite bad.
There isn't a cure (良药 ) for a cold, but you can take medicines to make you feel better. For example, you can take aspirin (阿司匹林) to get rid of your headache. It is good to rest, and to drink a lot of water, too. A doctor once told me, "With the right medicine, a cold will last for seven days. With no medicine, it will go on for a whole week!"
Where does our medicine come from? A long time ago, people understood that some plants made them feel better. They ate the leaves, the roots , the fruit or the seeds of plants. For example, the juice of lemons (柠檬) makes a sore throat feel better. In modern times, scientists have looked at these plants, and found out which chemicals (化学药品) are in them. Many of our medicines today are made from those chemicals. There are some diseases that we can't cure yet. And nobody has found a cure for old age. But because of modern medicines, the average (平均的) person now lives longer than their grandparents.
1. A cold often starts with________________.
A. a headache B. a cough C. a pain in your throat D. feeling a little cold
2. What should we do when we catch a cold?
A. We only take some medicine.
B. We should rest well, drink much water and have some medicine.
C. We just wait for a whole week.
D. We only need a good rest.
3. What makes a sore throat feel better?
A. The medicine aspirin. B. A lot of water.
C. Something inside lemons. D. The root of a plant.
4. What is the real meaning of the doctor's words?
A. There is almost no medicine that can cure the cold.
B. There is some medicine that can cure the cold.
C. You will feel well after a week when you take some medicine.
D. The cold is a serious disease.
高二英语阅读理解简单题查看答案及解析
When most of us look at our hands, we might notice that we need to clean, or stop biting our fingernails, and that’s about it. But if you ask a doctor, he can see a whole lot more. Everything from poor diet and stress to serious kidney (肾) problems can be revealed by a glance at your fingernails.
There are about 30 different nail signs that can be associated with medical issues, though may indicate more than one problem, according to Dr. Amy Derick, a clinical instructor of dermatology at Northwestern University.
Here are five of the things a doctor can tell about your health based on your fingernails.
1. People who aren’t eating well and lack vitamin or dietary may have thinner than normal nails, which are more likely to break.
2. Horizontal lines are associated with serious physical stress. They frequently occur in people who have gone through chemotherapy(化疗).They can also occur after some illnesses, injuries, or with severe malnourishment(营养不良).Interestingly, there may be an altitude connection too. They’ve also been found in people who dove 1,000 feet and others who participated in an Everest exploration.
3. Vertical lines, however, are generally not such a big deal. Some people are more genetically prone to them than others, but they’re commonly associated with aging.
4. When people lack iron, their nails can turn spoon-like. Instead of curving down and covering the finger normally, they ’ll start to rise up on the sides and front, like the part of a spoon that holds liquid.
5. Kidney and liver problems can create “half-and-half nails”, where one part of the nail is white and the other part dark or pink, according to Derick.
Doctors note that because disease diagnosis is complex and some symptoms can be associated with different diseases, you should always see a medical professional if you are concerned about something you notice.
1.What is the main idea of the passage?
A. Doctors can tell us something about our health by looking at our nails.
B. We should see a doctor if we find nails in bad condition.
C. A famous doctor in the USA conducted an interesting research.
D. If we don’t want to get ill, we need to clean and stop biting our fingernails.
2.If we don’t eat well or regularly, our fingernails may ________.
A. become harder than normal nails.
B. become thinner than normal nails.
C. become “half-and-half” nails.
D. have horizontal and vertical lines.
3.Who will have horizontal lines on the nails ?
A. A cancer patient who has received normal treatment.
B. Hungry African children suffering from severe malnourishment.
C. An explorer who had reached Zhangjiajie in Hunan Province.
D. A patient with serious illness, like kidney and liver problems.
4.Which of the following best describes the nails that show people lack iron?
A. The nails are thinner and more likely to break.
B. The nails will curve down and cover the fingers.
C. The nails will start to rise up on the sides and front.
D. The nails will change their colours on the surface.
高二英语阅读理解困难题查看答案及解析
Bill Javis took over our village news-agency at a time of life when most of us only want to relax. He just thought he would like something but not too much to do, and the news-agency was ready-made. The business produced little enough for him, but Bill was a man who only wanted the simplicity and order and regularity of the job. He had been a long-serving sailor, and all his life had done everything by the clock.
Every day he opened his shop at six a.m. to catch the early trade; the papers arrived on his door-step before that. Many of Bill’s customers were city workers, and the shop was convenient for the station. Business was tailing off by 10 o’clock, so at eleven sharp Bill closed for lunch. It was hard luck on anybody who wanted a paper or magazine in the afternoon, for most likely Bill would be down on the river bank, fishing, and his nearest competitor was five kilometers away. Sometime in the afternoon, the evening paper landed on the doormat, and at 4 o’clock Bill reopened. The evening rush lasted till seven, and it was worthwhile.
He lived in a flat above the shop, alone. Except in the very bad weather, you always knew where to find him in the afternoon, as I have said. Once, on a sunny afternoon, I walked home along the river bank from a shopping trip to the village. By my watch it was three minutes past four, so I was astonished to see Bill sitting there on his little chair with a line in the water. He had had no luck, I could see, but he was making no effort to move.
“What’s wrong, Bill?” I called out from the path.
For answer, he put a hand in his jacket and took out a big, golden object. For a moment I had no idea what it could be, and then it suddenly went off with a noise like a fire engine. Stopping the bell, Bill held the thing up and called back, “Ten to four, you see, and this is dead right.”
I had never known anyone carrying a brass alarm clock round with him before.
1.Bill Javis became a news-agent when ________.
A. he needed the money.
B. he decided to take things easy
C. he was quite an old man
D. he gave up clock-repairing
2.Bill opened the shop so early in the day because ________.
A. he liked to do as much as possible before he went to work
B. the shop had to be open when the morning papers came
C. he was never sure of time
D. it was then that he did a lot of business
3.On that sunny afternoon, the writer was surprised when he saw Bill because _______.
A. he thought it was late for Bill to be still fishing
B. he thought Bill was ill, since he was not moving at all
C. Bill had not caught anything, and that seemed strange
D. Bill stayed in his flat
4.What’s the meaning of the underlined phrase in paragraph 2?
A. become noisy B. become less
C. become stronger D. become busy
高二英语阅读理解中等难度题查看答案及解析
Bill Javis took over our village’s news-agency at a time of life when most of us only wanted to relax. He just thought he would like something but not too much to do, and the news-agency was ready-made. The business produced little enough for him, but Bill was a man who only wanted the simplicity and order and regularity of the job. He had been a long-serving sailor, and all his life had done everything by the clock.
Every day he opened his shop at 6:00 a. m. to catch the early trade; the papers arrived on his doorstep before that. Many of Bill’s customers were city workers, and the shop was convenient for the station. Business was tailing off by 10 o’clock, so at eleven sharp Bill closed for lunch. It was hard luck on anybody who wanted a paper or magazine in the afternoon, for most likely Bill would be down on the river bank, fishing, and his nearest competitor was five kilometers away. Sometimes in the afternoon, the evening paper landed on the doorway, and at 4 o’clock Bill reopened his shop. The evening rush lasted till seven, and it was worthwhile.
He lived in a flat above the shop, alone. Except in the very bad weather, you always knew where to find him in the afternoon, as I have said. Once, on a sunny afternoon, I walked home along the river bank from a shopping trip to the village. By my watch it was three minutes past four, so I was astonished to see Bill sitting there on his little chair with a line in the water. He had no luck, I could see, but he was making no effort to move.
“What’s wrong, Bill?” I called out from the path.
For answer, he put a hand in his jacket and took out a big, golden object. For a moment I had no idea what it could be, and then it suddenly went off with a noise like a fire engine. Stopping the bell, Bill held the thing up and called back, “Ten to four, you see, and this is dead right.”
I had never known anyone carrying a brass alarm clock round with him before.
1.Bill Javis became a news-agent when _______.
A. he needed the money
B. he was quite an old man
C. he decided to take up fishing
D. he gave up clock-repairing
2.Bill opened the shop so early in the day because _______.
A. he liked to do as much as possible before he went to work
B. the shop had to be open when the morning papers came
C. he was never sure of time
D. it was then that he did a lot of business
3.From the information given in the passage, who or what do you think was wrong?
A. The bell was－it must have gone off at the wrong time.
B. Bill was－he had dropped off to sleep.
C. The writer’s watch was－it was fast.
D. Bill’s clock was－it was old.
高二英语阅读理解中等难度题查看答案及解析
Social Phobia
It is natural to feel nervous, or shy in front of others at times. Most people manage to get through these moments when they need to. 1. It’s probably more than shyness. It may build up into a powerful fear. As a result, people feel uncomfortable participating in everyday social activities. This is called social phobia (also called social anxiety).
2. It prevents them from chatting with friends in the lunch time, joining an after-school club, or going to a party. Sometimes, they even feel too nervous to ask a question in class or go to a teacher for help. Social phobia not only prevents people from trying new things. It also prevents them from making the normal, everyday mistakes that may help people improve their skills even further
It is really sad, isn’t it? But the good news is that people with social phobia can learn to manage fear, develop confidence and communicating skills and stop avoiding things that make them nervous. Of course it’s not always easy. Dealing with social phobia takes the willingness patience and courage to face fears. 3.
Therapists (治疗师) can help people create a plan for facing social fears and build the skills and confidence to overcome it. And family or friends are especially important for them. 4.They can encourage them to pick a small goal to aim for, remind them to go for it, and be there when they might feel discouraged.
Little by little, someone who decides to deal with extreme shyness can learn to be more comfortable. 5. As shyness and fears begin to melt, confidence and positive feelings build. Pretty soon, the person is thinking less about what might feel uncomfortable and more about what might be fun.
A. Friends can overcome their fears easily.
B. But for someone, the anxiety can be extreme.
C. They are not able to make eye contact with classmates.
D. Social phobia makes people lonely or disappointed over missed opportunities.
E. Each small step forward helps build enough confidence to take the next small step.
F. It also takes an action to go forward rather than back away when feeling shy.
G. The support from those key people helps them gather the courage to try something new.
高二英语七选五困难题查看答案及解析
根据短文内容,从短文后的选项中选出能填入空白处的最佳选项.选项中有两项是多余的.
1._____
Most of us have one or a few bad habits that we’d like to get out of. But how do you do it? I have a few suggestions that have help you and people around me. Here are some tips that can help you to finally get out of that bad habit.
__2.__.If you tell people around you that you will stop smoking or start to exercise three times a week, then they will check up on you. And you will feel you have to keep your promise because it is let out into the world.
Avoid temptations （诱惑）. ___3.__. Places where you are likely to spend too much money . Things in your cupboard that will not help you to get healthier and you should not have at home at all. And people that drag(拉) you down and back into your old ways.
__4.__ . It may seem like a good idea to change your life all at once. In our daily life , stress and lack(缺乏) of energy usually lead to failure. Don’t try to be Superman or Wonder Woman. Take it easy and break one habit at a time.
___5.___. You will probably not succeed the first time you do it. You fail and you make mistakes when you make changes and try new things. That’s just life and nothing to feel bad about. What should you do next is to try again.
A. Know what usually gets you into bad habits.
B. Simple tips for getting out of bad habits.
C. See your future in your mind.
D. If at first you don’t succeed, please try again.
E. Tell your friends and family .
F. The reason why we need to make good habits.
G. Don’t break more than one habit at a time.
高二英语七选五中等难度题查看答案及解析