2. 公务员
  3. Throughout history man has had to accept the fact that all living things must die. But people now live longer than they【C1】_____

Throughout history man has had to accept the fact that all living things must die. But people now live longer than they【C1】_____

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问题     Throughout history man has had to accept the fact that all living things must die. But people now live longer than they【C1】______. Yet, all living things still show the【C2】______of aging, which will eventually【C3】______death.
    Aging is not a disease, but as a person passes maturity(成熟期), the cells of the body and the 【C4】______they form do not function as well as they【C5】______in childhood and teenage years. The body provides less【C6】______against disease and is more【C7】______to have accident.
    A number of related causes may【C8】______aging. Some cells of the body have a fairly long life, but they are not【C9】______when they die. As a person ages, 【C10】______of brain cells and muscle cells decreases. 【C11】______body cells die and are replaced by new cells. In an aging person the【C12】______cells may not be as workable or as capable【C13】______growth as those of a young person.
    Another【C14】______in aging may be changes within the cells【C15】______. Some of the protein chemicals in cells are known【C16】______with age and become less elastic(有弹性的). This is why the skin of old people wrinkles(皱纹) and【C17】______. This is also the reason why old people 【C18】______in height. There may be other more important chemical changes in the cells. Some complex cell chemicals, such as DNA and RNA, store and【C19】______information that the cells need. Aging may affect this【C20】______and change the information – carrying molecules so that they do not transmit the information as well.
【C5】
选项 A、do
B、has done
C、did
D、had done
答案C
解析 此句中的did是用来代替前面的动词function，以避免重复。因为这里有一个表示过去的时间状语in childhood and teenage years，所以只能用一般过去时。
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