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  3. Parents of children who happily eat what’s put in front of them might assume their kids are well nourished. But two new studies

Parents of children who happily eat what’s put in front of them might assume their kids are well nourished. But two new studies

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问题     Parents of children who happily eat what’s put in front of them might assume their kids are well nourished. But two new studies drive home the importance of varying that diet. Deficiencies of vitamin D, omega-3 fats, and other healthful compounds are common; it turns out—and consequential.
    Growing evidence links vitamin D deficiency not only to weak bones but also to impaired immunity, asthma, and diabetes among other problems. And some of the latest research finds that rates of asthma and related respiratory problems climb in kids who are short on other commonly missing essentials, including vitamins C and E and omega-3 fatty acids.
    A team at the Harvard School of Public Health evaluated the diet and respiratory(relating to the process of breathing)health of some 2,000 North American high school seniors and found that teens who lack of fruit, vegetables, and other healthful foods were most likely to have problems such as coughing, panting, episodes of bronchitis, and asthma.
    Vitamins C and E, which are abundant in fruit and dark-green vegetables, may "protect the lung from stress," says Harvard research fellow and study leader Jane Burns. Omega-3 reduces inflammation, a key feature of asthma, in which airways swell and make breathing difficult. Oily fish like salmon, mackerel, and tuna—as well as cod-liver oil—are rich in both omega-3 and vitamin D. Vitamin D can also be obtained from multivitamin milk and sunshine—and many kids should be getting more of both.
    In another new study, researchers found that 55 percent of outwardly healthy children and teenagers they tested didn’t have enough vitamin D to grow healthy bones. Dark-skinned children were particularly likely to be short of the bone-building vitamin, according to Babette Zemel, an author of the study and director of the Nutrition and Growth Laboratory at Children’s Hospital of Philadelphia. The melanin(a natural dark brown colour in human skin, hair, and eyes)that makes their skin dark also blocks ultraviolet rays, which the body uses to make vitamin D. In winter, when the sun was weakest, more than 90 percent of blacks in the study were vitamin D deficient.
    Researchers suggest pointing kids outside, and waiting a few minutes before putting on sun block; 10 minutes of midday summer sun provides 10,000 international units of the vitamin—more than enough for a day. Like melanin, sunblock prevents the skin from making vitamin D, so a bit of lotion-free exposure is necessary to grab the benefit.
According to the text, dark-skinned kids are particularly short of vitamin D in that the dark skin
选项 A、has more melanin that consumes more vitamin D.
B、absorbs more ultraviolet rays, thus killing the melanin.
C、can only produce units of the vitamin when the sun was strong.
D、has more melanin that blocks ultraviolet rays, reducing vitamin D production.
答案D
解析 事实细节题，考查因果细节。根据题干的dark-skinned kids定位到第五段。该段讲到黑色素同时也阻挡紫外线，而紫外线是人体合成维生素D的来源。故选D。
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