There is no living creature that does
not need sleep or complete rest every day. If you want to know why, just try{{U}}
(41) {{/U}}without sleep for a long period of time! You{{U}} (42)
{{/U}}discover that your mind and body would become{{U}} (43)
{{/U}}tired to work properly. You would become irritable and find it hard to
think clearly or{{U}} (44) {{/U}}on your work. So sleep is quite{{U}}
(45) {{/U}}the time when the cells of your body{{U}} (46)
{{/U}}from the work of the day and{{U}} (47) {{/U}}supplies of
energy for the next{{U}} (48) {{/U}}of activity. One of
the things we all know about sleep is that we are{{U}} (49) {{/U}}in
sleep. We do not know what is{{U}} (50) {{/U}}on around us. But that
does not mean the body stops{{U}} (51) {{/U}}activity. The vital organs
continue to work during sleep, but most of the body functions are{{U}} (52)
{{/U}}down. For example, our breathing becomes slower and
deeper. The heart beats{{U}} (53) {{/U}}slowly, and the blood pressure
is lower. Our arms and legs become limp(软弱的), and muscles that control our
posture(姿势) are{{U}} (54) {{/U}}. It would be impossible for our body to
relax to such an{{U}} (55) {{/U}}if we were awake. So sleep does for
us{{U}} (56) {{/U}}the most quiet rest cannot do. Your
body temperature becomes lower when you are asleep,{{U}} (57) {{/U}}is
the reason people go to sleep under some kind of{{U}} (58) {{/U}}. And
even though you are unconscious, ninny of your reflexes (反射作用) still work.{{U}}
(59) {{/U}}, if some one tickles your foot, you will pull it away in
your sleep, or even{{U}} (60) {{/U}}a fly from your forehead. You do
these things without knowing it.
【正确答案】
C
【答案解析】try to do努力做某事；try doing试着做某事。根据上下文“如果你想知道为什么会这样，不妨试着长时间不睡觉”，B，D项不符合本句结构，A项不符合句意。