有关地球圈层的正确说法是[ ]
A、大气圈中的臭氧主要集中在对流层
B、水圈是连续而规则的圈层
C、岩石圈位于软流层之上
D、各圈层有明显的界线
答案：C
—Do you know ______ last night?
—Sorry , I don't know. But I think he should go to bed early
because he will have an English exam this afternoon. [ ]
A. when he goes to bed
B. when he went to bed
C. when did he go to bed
D. when does he go to bed
留置权中，债权的发生与该动产的占有( )。
A．没有关系 B．有顺序关系C．有唯一性关系 D．有牵连关系
