Throughout history man has had to accept the fact that all living things must die.But people now live longer than they（21）. Yet, all living things still show the （22）of aging, which will eventually result （23）death. Aging is not a disease, but as a person passes maturity, the （24）of the body and the organs they （25）do not function as well as they did in childhood and adolescence. The body provides less strength（26）disease and is more（27）to have an accident. A number of related causes may （28）aging. Some cells of the body have a fairly long life,but they are not（29） when they die. As a person ages,（30）of brain cells and muscle cells decreases. Other body cells die and are replaced by new cells. In an aging person the（31）cells may not be so capable （32）growth as（33）of a young person. Another （34）in aging may be changes within the cells themselves. Some of the protein chemicals in cells are known （35）with age and become less elastic.This is（36）the skin of old people wrinkles and becomes（37）.This is also the reason why old people shrinks in（38）.There may be other more chemical changes in the cells. Some complex cell chemicals, such as DNA and RNA.store and（39）information that the cells need.Aging may affect this（40）and change the molecules carrying information so that they do not transmit information as well.