英语专业四级考试指南 test 7

　　How and Why We Sleep?
It's apparent that everyone needs to sleep.However,most people vary think about how and why they sleep.We know that if we sleep well,we felt rested.If we don't sleep enough,we often felt tired and irritable¹.It seems there are two poposite of asleep:physical rest and emotional and psychological rest.We need to rest our bodies and our minds. Both of which are important in order for us to be healthy.
Each night we alternative between two kinds of sleep:active sleep and passive sleep.The passive sleep gives our body the rest and prepares us for active sleep.In which dreaming occurs throughout the night,people alternative between passive and active sleep.They bring rests then they becomes active and dreaming occurs.The psycho is repeated several times throughout the night.During eight hours of asleep,people dream for a total of one and a half hours on the average.

1 irritable   

adj.急躁的；过敏的；易怒的

参考例句：

• He gets irritable when he's got toothache.他牙一疼就很容易发脾气。
• Our teacher is an irritable old lady.She gets angry easily.我们的老师是位脾气急躁的老太太。她很容易生气。