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Millions of Americans take large amounts of vitamin C pills every day because they believe the vitamin will help them stay healthy. However, a new study says vitamin C may help produce substances that can damage DNA. Scientists at the University of Pennsylvania experimented with vitamin C in test tubes. They studied the effects of vitamin C on a substance produced in the body from fat. That substance is called hydro-peroxide（过氧化氢物）, which can be changed in a cell into substances that can damage DNA. The scientists found that vitamin C easily changed the hydro-peroxide into the gene-damaging poisons. Such damage is the first step toward developing cancer.However, the scientists say the study does not mean that vitamin C causes cancer. They say it is well-known that vitamin C is important for human health, but people can get enough vitamin C in the foods they eat. Earlier studies have shown that eating a lot of fruits, vegetables and grains can reduce the chance of developing both heart disease and cancer.Other researchers agree that the latest study is important in understanding the chemistry of vitamin C. But they say the study did not involve people. The vitamin C was tested in the laboratory only. They think the results might be different in living cells.Mark Levine is a vitamin C expert who questions whether a similar study in people would produce the same results. He also says people should get their vitamin C in food instead of taking huge amounts in pills to stay healthy, and research does not support taking a lot of vitamin C.The United States government says people should get about eighty milligrams of vitamin C each day in the foods they eat. Studies have shown that the body cannot use more than two hundred milligrams of vitamin C each day. Medical researchers say that taking vitamin C pills cannot replace the value of eating healthy foods.1.What does this passage mainly discuss?2.Which one is Not true about the effect of VC according to the passage?3.What does the author imply when he mentions “living cells” in Paragraph 3?4.Which of the following is not true about the scientists’ research?5.Taking a lot of VC （）.

George （）an agonizing 48-hour wait for the results of the tests.

（）students should be motivated by a keen interest in theatre and should have some familiarity with plays in production.

The number 30 on a road sign （）that the speed limit is 30 miles an hour.

A firm might sometimes sell at a loss to drive a competitor out of business, and （）increase its market power.

There are several possible explanations for the great job （）in Japan in contrast to the great job mobility in the United States.

To be （）with you, I think you’re making a dreadful mistake by refusing to cooperate.

I will hold you personally （）if anything goes wrong in this project.

A computer file is a collection of （）data, used to organize the storage and processing of data by computer.

The offer of a free overseas tour （）him into buying the villa on the hillside.

I admire her courage, compassion and （）to the cause of humanity, justice and peace.

Is it true that the company is going bankrupt? I didn’t mean to eavesdrop what you said. I just （）it.

The car, at least as we know it, is on the way out, because its exhaust （）a threat to the environment.

We must get the trapped victims out at once because the building is in （）danger of an explosion.

Democratic government is a phrase that is notoriously hard to （）.

The republication(再版)of the poet’s most recent works will certainly （）his national reputation.

You can （）the video camera on a tripod（三脚架），so that you don't have to worry about holding it steady while you ask questions.

I’m pleased to hear of your job offer——all that hard work at school has obviously （）.

Parks and open spaces are essential to the quality of life in dense （）areas such as New York City.

His total worldly possessions （）little more than the clothes he stood up in.

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