A._______ of us is perfect; we all may make mistakes. ……

单项选择题-- Has Mary finished writing her article?-- No, and it _____ before class was over.A.should be finished B.should finish C.should have finished D.ought to have been finished

单项选择题Only after the second tower of the World Trade Centre did people know it was not an accident, but an attack of some kinD. A.had hit B.did fall C.was hit D.was fallen 

单项选择题__ , she knew she'd never been there beforE.

单项选择题We were just about to leave_______ it started to snow.A.when B.before C.after D.since

单项选择题The dish_____ nice , but the milk _____ sour.A.is smelt , is smelt B.is smelt , smells C.smells , is smelt D.smells , smells