Throughout history man has had to accept the fact that all living things must die, but people now live longer than they（1）. Yet, all living things still show the __（2）of aging, which will eventually（3）death.
Aging is not a disease, but as a person passes maturity, the cells of the body and the organs they form do not function as well as they did in childhood. The body provides less（4）against diseases and is more inclined（5）accident.
A number of related causes may contribute to aging. Some cells of the body have a fairly long life, but they are not（6）when they die. In an aging person the new cells may not be as capable（7）growth as those of a young person.
Another（8）in aging may be changes within the cells themselves. Some of the protein chemicals in cells are known to change with age and become less flexible. This is why the skin of old people wrinkles. This is also the reason old people（9）in height. There may be other more important chemicals changes in the cells. Some complex cell chemicals, such as DNA and RNA, store and（10）information that the cells need. Aging may affect this process and change the information-carrying molecules so that they do not transmit the information as well.
（5）下列正确的是（ ）

A.to

B.for

C.against

D.from