why we must sleep

why we must sleep very early can make us better? why don't we sleep? Why do we need sleep Why must we go to bed? why must we save our earth 作文 No one knows why we sleep,but it iscertain that we need to.P That is why we must not waste time. ( ) we __enough sleep to study well.A.must B.can C.need D.ma 英语翻译This is not good for them.We must sleep at night when it 英语翻译Most people rarely think about how or why they sleep.We why don't you sleep We must