单选题：The students entered the classroom, smiling and ______, and ..

—What did you say to your sister? I saw her crying in the room.— It _________ my fault. I just said hello to her when I met her, nothing else.A．must have beenB．can’t have beenC．oughtn’t to beD．should have been

指出错误并改正。 1. I fell in love with the city the first time when I visited it. ____________________________________________________________ 2. No matter how the job is difficult, I'm determined to finish it on schedule. _________________________________

Some economists predict that the dollar will remain weak _____ economies abroad are expected to growfaster than that of the United States.A. while B. as C. before D. until

Americans and Canadians can understand each other ______ they don't speak the same kind of English.A. now that B. even if C. as if D. only if

Lora，you ____________ leave all your books on the floor like this!A．wouldn’tB．mustn’tC．needn’tD．may not