2. 外语
  3. Between now(June) and Labor Day, millions of American will offer up their bodies to the sun’s rays. A tan indicates health and b

Between now(June) and Labor Day, millions of American will offer up their bodies to the sun’s rays. A tan indicates health and b

admin2011-01-06  62
问题     Between now(June) and Labor Day, millions of American will offer up their bodies to the sun’s rays. A tan indicates health and beauty, and most sun worshippers will sacrifice a lot to achieve it—including themselves. With each hour, the sun’s ultraviolet radiation produces irreversible damage, hastening the development of unsightly wrinkles. And with each year on the beach or rooftop, the sunbather increases his risk of getting skin cancer.
    Skin cancer is by far the most common form of cancer. An estimated 400000 new cases will be detected this year in the United States, and almost all of them can be blamed on overexposure to the sun. Fortunately, most of these cancers are highly curable. But they can be disfiguring and take time to treat. For that reason, sun worshippers should treat deity with a good deal of awe.
    Sunburn, of course, is the initial hazard posed by UV radiation. Prolonged exposure to UV, however, interferes with the production of collagen fibers in the dermis, causing the skin to lose elasticity and creating premature wrinkles. Further deterioration of the dermis deprives the epidermis of nutrition and causes it to become thin and dry.
    Cancer is UV’s final insult. Short-wave radiant energy, especially from the UV-B band, breaks the strands of DNA. Enzymes work constantly to rearrange the DNA into proper sequence, but with repeated UV exposure, the repair process may eventually break down. Then the mutant DNA may produce a colony of cancer cells.
    But skin cancer may be avoided with a good dose of common sense. People with fair skin and blue eyes who burn easily stand the highest risk. Special danger spots are the parts of the body most constantly exposed to the sun, such as the cheeks, nose, lower lip and the ears. People who have already developed precancerous lesions or had one skin cancer growth stand a greatly increased chance of developing others. Dermatologists recommend avoiding the sun when it is most intense—between 11 a.m. and 3 p.m. Anyone who insists on sunbathing should use a good sun screen. These lotions and salves contain chemicals, such as paraaminobenzoic acid, that block out the burning UV-B radiation while permitting the tanning rays to reach the skin.  
Why does the repair process of the DNA may finally fail?
选项 A、Because short-wave radiant energy breaks the strands of the DNＡ.
B、Because the DNA may produce a colony of cancer cells.
C、Because enzymes work to rearrange the DNA into a new order.
D、Because the patient is exposed to UV form time to time.
答案D
解析 第四段中“…but with repeated UV exposure，the repair process may eventually break down”与D项的内容一致。
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