Everyone needs to sleep. If we don’t sleep enough, we often
feel tired and irritable (烦躁的，易恕的). It seems there are two purposes of sleep:
active sleep and passive sleep. The passive sleep gives our body the rest that
is needed, and prepares us for active sleep, in which dreaming occurs. In
passive sleep, the body is at rest. The heat slows down. The body processes
become very slow. We move very little. And the brain becomes very inactive. If a
person continues to sleep, she or he enters a new stage, a more active stage.
The body goes through several changes: the brain temperature rises, the amount
of blood in brain increases, the body becomes very still and the brain becomes
active, the eyes begin to move rapidly, and the person is dreaming.
Throughout the night, people alternate between passive and active sleep.
During eight hours of sleep, people dream for a total of one and a half hours on
the average. Many people say that they don’t dream, or that they
rarely dream. Doctors have studied the sleep cycles and have found that everyone
dreams--in fact, that everyone needs to dream in order to rest his or her
mind. There are (46) purposes of sleep: active sleep and
passive sleep. In (47) sleep, the body processes become
very slow. In (48) sleep, dreaming occurs. In active
stage, (49) becomes active. People need active sleep to
help them (50) .