填空题 There is no living creature that does not need sleep or complete
rest every day.
If you want to know why, just try go without sleep for a long period 67. ______
of time. You will discover that your mind and body would become tired 68. ______
to work properly. You would find it hard to think clearly or concentrate in 69. ______
your work. So sleep is quite simply the time when the cells of your body
recover from the work of the day and build up supplies of energy for
the latter period of activity. 70. ______
One of the things we all know about sleep is that we are
unconscious in sleep. We do not know what is going up around us. But 71. ______
that doesn't mean the body stops all activity. The important organs stop 72. ______
to work during sleep, but most of the body functions are slowed down.
For example, our breathing becomes quicker and deeper. The heart 73. ______
beats more slowly, and the blood pressure is lower. Our arms and legs
become limp (柔软的) and muscles are rest. It would be impossible for 74. ______
our body to relax to such an extent if we were awake. So sleep does for
us that the most quiet rest can not do. 75. ______
And even though you are unconscious, many of your reflexes (习
惯性思维) still work. For instance, if someone tickles (使……觉得痒)
your foot, you will put them away in your sleep. You do this without 76. ______
knowing it.