Vitamin D helps our bodies make a special che...

Vitamin D helps our bodies make a special chemical，and this special chemical, ______

affects our brains，making us feel happy．

A．in turn          B．in particular         C．in advance         D．in short

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Vitamin D helps our bodies make a special chemical，and this special chemical，

__________，affects our brains，making us feel happy.

A. in turn            B. in particular         C. in advance    D. in short

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(2014·烟台市第二次诊断)Vitamin D helps our bodies make a special chemical，and this special chemical，________，affects our brains，making us feel happy.

A．in turn　    B．in particular

C．in advance　    D．in short

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Vitamin C helps our bodies make a special chemical, which _______ affects our brains, making us feel happy.

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This new kind of chemical will help keep the air, soil and water________ from pollution．

A．empty                 B．loose                C．free              D．short

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Chemicals in the body ______our food _____ into useful things．

A．break, into                                      B．break, up

C．break, down                                    D．break, off

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Chemicals in the body ______our food _____ into useful things．

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Chemicals in the body______________ our food into useful substance.

A. mix up B. deal with  C. bring in  D. break down

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Vitamin D helps bones and muscles grow strong and healthy．Low levels of vitamin D can lead to diseases such as rickets(软骨病), mainly found in children．The thinning of bone is a common problem as people, especially women, get older．

But more and more research is suggesting that vitamin D might also help prevent many diseases．The easiest way to get vitamin D is from sunlight．The sun’s ultraviolet(紫外线的)rays react with skin cells to produce vitamin D．But many people worry about getting skin cancer and skin damage from the sun．As a result they stay out of the sun．Also, darker-skinned people produce less vitamin D than lighter-skinned people．The amount also de-creases in older people and those living in northern areas that get less sunlight．

Not many foods naturally contain vitamin D．Foods high in this vitamin include oily fish and fish liver oils．Farmed fish have only about one-fourth as much vitamin D as wild fish．Small amounts of vitamin D are found in beef liver, cheese and egg yolks．But most of the vitamin D in the American diet comes from foods such as milk．

Research in the last several years has shown that low levels of vitamin D may increase the risk of heart attacks in men and deaths from some cancers．More doctors are now having their patients tested for their vitamin D levels．But as research continues, some experts worry that if people take too much vitamin D, it might act as a poison, Also, skin doctors warn people be careful with sun exposures because of the risk of skin cancer．

1.The first paragraph is mainly about________．

A．the muscle diseases                        B．the sources of vitamins

C．the importance of health                    D．the functions of vitamin D

2.Which of the following people produce the least amount of vitamin D?

A．Elderly darker-skinned people．

B．Young lighter-skinned people．

C．Elderly lighter-skinned people．

D．Young darker-skinned people．

3.People can get the most vitamin D from________．

A．beef liver           B．cheese               C．wild fish           D．farmed fish

4.What can we infer from the text?

A．Being exposed to sunlight is the safest way to get vitamin D

B．Lack of vitamin D can make people age quickly

C．Proper vitamin D levels people need are still not determined now．

D．The vitamin D level is higher in men than in women．

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Special trees that grow faster, fight pollution, produce better wood, and even sense chemical attacks are being planted by scientists in the US．

When 40 per cent of Hawaii's US$14 million-a-year papaya （木瓜）industry was destroyed by a virus five years ago, work began on creating genetically engineered（转基因的）trees．

Researchers successfully introduced seeds that were designed to resist the virus．Since then, more and more people have been testing genetically engineered trees．Some researchers put special bacteria into trees to help them grow faster and produce better wood．Others are trying to create trees that can clean polluted soil．Meanwhile fruit farmers are looking for trees that are strong enough to resist worms, and paper companies want trees that produce more wood and therefore more paper．

The Pentagon （五角大楼） even gave the researchers US$500,000 this year after they developed a pine tree that changes its colours if it senses a chemical attack．So far, the poplar, eucalyptus （杨树与桉树）, apple and coffee trees are among those being engineered．All this can be done today because we have a better understanding of tree genomes （基因组）．

However, some people fear that the genetically engineered trees will cause dangerous results．They are worried that the new trees will breed with natural species and change the balance of the forest environment．

“It could be destructive,” said Jim Diamond, an environmentalist. “Trees are what is left of our natural environment and home to many endangered species.”

But researchers insist that science could give nature a fighting chance against both natural and man-made dangers．They hope to answer the critics by stopping the new trees from breeding, so their effect on the environment can be controlled．

63．Which kind of tree is not the ones that scientists are planting in the US?

A．Trees that worms can't hurt．

B．Genetically engineered trees．

C．Trees that can resist wind better．

D．Trees that can protect themselves at a chemical attack．

64．What caused the American scientists to work on special trees?

A．Tree genomes are mapped out so scientists know how to improve trees．

B．Great numbers of trees have been lost due to attacks by viruses．

C．Researchers successfully introduced seeds designed to resist the virus．

D．They think science could give nature a fighting chance against both natural and man-made dangers．

65．Which of the following was probably the first kind of trees being engineered?

A．Papaya．                     B．Pine．                           C．Apple．                        D．Poplar．

66．Why did critics think engineered trees dangerous? Because ________．

A．these trees can destroy the balance of nature

B．everything except trees has been genetically engineered

C．trees are home to many endangered species

D．these trees may affect normal trees

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