— Will you read me a  story, Mummy?

— OK.You _____ have one if you go to  bed as soon as possible.    [ ]

A. might                      

B. must    

C. could                      

D. shall

曝气池的实际水力停留时间与（）有关。

A.来水水量

B.来水水质

C.曝气池的有效容积

D.回流污泥量