完形填空。（共20小题；每小题1.5分，满分30分）
Throughout history man has had to accept the fact that all living things must die. But people now live longer than they 36 . Yet, all living things still show the  37 of aging, which will eventually 38 deaths.
Aging is not a disease, but as a person passes maturity（成熟期）,the cells of the body and the 39 they form do not function as well as they 40 in childhood and teenage years. The body provides less 41 against disease and is more 42 to have accident.
A number of related causes may 43 to aging. Some cells of the body have a fairly long life, but they are not 44 when they die . As a person ages, 45 of brain cells and muscle cells decreases. 46. body cells die and are replaced by new cells. In an aging person the 47 cells may not be as workable or as capable 48 growth as those of a young person.
Another 49 in aging may be changes within the cells 50.Some of the protein chemicals in cells are known to 51 with age and become less elastic（有弹性的）.This is why the skin of old people wrinkles（皱纹）and hangs 52 . This is also the reason why old people 53 in height. There may be other more important chemical changes in the cells. Some complex cell chemicals, such as DNA an RNA, store and 54 information that the cells need. Aging may affect this 55 and change the information-carrying molecules so that they do not transmit the information as well.
36. A. would                       B. be used to             C. used to                  D. used
37. A. function          B. effect                     C. affect                     D. sign
38. A. lead in             B. give in           C. run into                  D. result in
39. A. hands                       B. feet                         C. heart             D. organs
40. A. made      B. took                   C. did        D. remembered
41. A. energy     B. protection        C. vigor      D. power
42. A. likely       B. probable           C. possible                 D. alike
43. A. attend      B. contribute        C. add       D. devote
44. A. replaced     B. reborn     C. recovered          D. surrendered
45. A. a number    B. the amount   C. the number          D. a great deal
46. A. The others         B. the other        C. Another           D. Other
47. A. old        B. left              C. new              D. other
48. A. to          B. for               C. of                     D. in
49. A. factor                  B. effect             C. reason          D. element
50. A. it                  B. them     C. themselves         D. that
51. A. become            B. turn       C. change            D. get
52. A. loose                  B. high              C. large      D. fat
53. A. increase               B. shrink                C. lengthen              D. decrease
54. A. pass away    B. pass by      C. pass off     D. pass on  
55. A. improvement         B. procession           C. approach          D. process