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  3. Smoking causes wrinkles by upsetting the body’ s mechanism for renewing skin, say scientists in Japan. Dermatologists say the fi

Smoking causes wrinkles by upsetting the body’ s mechanism for renewing skin, say scientists in Japan. Dermatologists say the fi

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问题     Smoking causes wrinkles by upsetting the body’ s mechanism for renewing skin, say scientists in Japan. Dermatologists say the finding confirms the long-held view that smoking ages skin prematurely.
    Skin stays healthy and young-looking because of a fine balance between two processes that are constantly at work. The first breaks-down old skin while the second makes new skin. The body breaks down the old skin with enzymes called matrix metalloproteinases, or MMPs, They chop up the fibers that form collagen(胶原质)—the connective tissue that makes up around 80 percent of normal skin.
    Akimichi Morita and his colleagues at Nagoya City University Medical School suspected that smoking disrupted the body’ s natural process of breaking down old skin and renewing it. To test their idea, they first made a solution of cigarette smoke by pumping smoke through a saline(盐的)solution. Smoke was sucked from cigarettes for two seconds every minute. Tiny drops of this smoke solution were added to dishes of human fibroblasts, the skin cells that produce collagen.
    After a day in contact with smoke solution, the researchers tested the skin cells, to see how much collagen-degrading MMP they were making. Morita found that cells exposed to cigarette smoke had produced far more MMP than normal skin cells.
    Morita also tested the skin cells to see how much new collagen they were producing. He found that the smoke caused a drop in the production of fresh collagen by up to 40 percent.
    He says that this combined effect of degrading collagen more rapidly and producing less new collagen is probably what causes premature skin ageing in smokers, in both cases, the more concentrated the smoke solution the greater the effect on collagen. " This suggests the amount of collagen is important for skin ageing," he says. "It looks like less collagen means more wrinkle formation".
    Morita doesn’ t know if this is the whole story of why smokers have more wrinkles. But he plans to confirm his findings by testing skin samples from smokers and non-smokers of various ages to see if the smoking has the same effect on collagen. "So far we’ ve only done this in the lab. " he says. " We don’t know exactly what happens in the body yet that might take some time. "
    Other dermatologists are impressed by file work. "This is fascinating," says Lawrence Parish. Director of the Centre for International Dermatology at Thomas Jefferson University Hospital in Philadelphia. This confirms scientifically what we’ve long expected, he says. "Tobacco smoke is injurious to skin. "
Healthy skin lies in______.
选项 A、a well-kept balance between two working processes
B、the two processes of breaking down skin cells
C、a fine balance in the number of cigarettes
D、the two steps of forming collagen
答案A
解析 文章第二段第一句提到了Skin stays healthy and young—looking because of a fine balancebetween two processes that are constantly at work．即皮肤不断地进行着新陈代谢，故保持健康和年轻的状态。
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