Sunlight is a great source of vitamin D in most of the world. Yet a (an)【C1】

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问题 Sunlight is a great source of vitamin D in most of the world. Yet a (an)【C1】______number of experts think that many people aren’t getting enough vitamin D—【C2】______those who work and play indoors.
It’s long been known that vitamin D is【C3】______for strong bones. Research in the last several years has shown that low levels of vitamin D may increase the risk of heart【C4】______in men and deaths from some cancers. But new research suggests that it also protects against a wide【C5】______of diseases. Low levels of vitamin D have also been【C6】______with various forms of cancer and high blood pressure, stroke,【C7】______illness etc. The strongest source,【C8】______far, is ultraviolet (紫外线) B rays from the sun, which【C9】______a form of cholesterol (胆固醇) into vitamin D in the skin. But UVB rays【C10】______greatly depending on cloud cover, time of year and time of day. Dark-skinned and elderly people don’t【C11】______vitamin D from the sun as【C12】______as younger, fair-skinned people. UVB rays also don’t【C13】______glass or sunscreen with a factor of 8 or more. It’s difficult to get much vitamin D through diet. Few foods【C14】______it naturally. It’s widely【C15】______that most people need some supplemental vitamin D—the question is, how much? Current U. S. guidelines, issued in 1997,【C16】______for 200 international units from birth through age 50. The National Osteoporosis Foundation【C17】______adults over age 50 to get at least 800 to 1,000 IUs to【C18】______against fractures (骨折).
But as some experts research carry【C19】______the experiment, they worry that if people take too much vitamin D, it might act as a poison. Also, skin doctors warn people to be careful with sun【C20】______because of the risk of skin cancer. [br] 【C18】

选项 A、guard
B、take
C、set
D、count

答案 A

解析动词词组辨义题。前面提到“全美骨质疏松症基金会建议50岁以上的成年人每天至少补充800一1000IU的维生素”，目的是“防止发生骨折”，guard against“防止，提防”符合题意。take against“反对，不喜欢”；set against“反对，使对立，使平衡”；count against“不利于”，均不符合文意，故排除。

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