— Who is the girl standing over there? 

— Well, if you _____ know, her name is Mabel. [ ]

A. may

B. can

C. must

D. shall

管道系统正确的吹洗顺序是()。

A.支管ー疏排管ー主管 

B.疏排管ー支管ー主管 

C.主管ー支管ー疏排管 

D.主管ー疏排管ー支管