II. 完形填空（共20小题；每小题1分，满分20分）阅读下面短文，掌握其大意，然后从   21—40题各题所给的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项。
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  23   death.
Aging is not a disease, but as a person passes maturity (成熟期), the cells of the body and the  24   they form do not function as well as they   25  in childhood and teenage years. The body provides less   26  against disease and is more   27  to have 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.  31   body cells die and are replaced by new cells. In an aging person the  32  cells may not be as workable or as capable  33   growth as those of a young person.
Another   34   in aging may be changes within the cells   35  . Some of the protein chemicals in cells are known   36  with age and become less elastic (有弹性的). This is why the skin of old people wrinkles (皱纹) and   37 . This is also the reason why old people   38   in height. There may be other more important 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 information-carrying molecules so that they do not transmit the information as well.
21. A．would             B．be used to               C．used to            D． used
22. A．function      B．effect             C．affect         D． appearance
23. A．lead in        B．give in                    C．run into          D． result in
24. A．hands         B．feet                       C．heart             D． organs
25. A．do           B．has done               C．did               D． had done
26. A．energy       B．protection            C．vigor         D． power
27. A．likely         B．probable              C．possible          D． alike
28. A．attend to       B．contribute to         C．add to          D． devote to
29. A．replaced      B．reborn                 C．recovered     D． surrendered
30. A．a number      B．the amount          C．the number   D． a great deal
31. A．The others          B．The other         C．Another       D． Other
32. A．old           B．left                          C．new          D． other
33. A．to           B．for                    C．of            D． in
34. A．factor         B．effect                        C．reason          D． element
35. A．for themselves B．of themselves       C．themselves    D． on their own
36.   A．change         B．to have changed    C．to change     D． to be changed
37. A．hangs loose   B．hangs loosely      C．is hanging loosely    D．is hanging loose
38. A．increase        B．shrink                 C．lengthen       D． decrease
39. A．pass away     B．pass by                C．pass off        D． pass on
40. A．improvement  B．procession           C．approach      D． process