[单项选择]

Everyone needs to sleep. If we don’t sleep enough, we often feel tired and irritable (易怒的).It seems there are two purposes of sleep: physical rest and emotional rest. We need to rest our bodies and our minds. Both are important in order for us to be healthy.
Each night we alternate (交替) between two kinds 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 heart 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 thro, gh several changes: the brain temperature rises, the amount of blood in brain increases, the body becomes very still and the brain becomes active. And as the brain becomes more active, the eyes begin to move rapidly, and the person is dreaming.
Th
A. to rest our bodies
B. to rest our arms and legs
C. to become less angry
D. both A and B