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   death.
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   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   51   with age and become less elastic (有弹性的). This is why the skin of old people wrinkles (皱纹) and   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 and 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．do            B．has done         C．did          D． had done
41. A．energy        B．protection     C．vigor            D． power
42. A．likely            B．probable        C．possible    D． alike
43. A．attend to       B．contribute to  C．add to    D． devote to
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．for themselves          B．of themselves   C．themselves        D． on their own
51.   A．change           B．to have changed  C．to change         D． to be changed
52. A．hangs loose   B．hangs loosely     C．is hanging loosely D． is hanging loose
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