1.(2011全国卷,32) They have arrived at lunchtime but their flight was delayed.
A.will B.can C.must D.should
答案 D
解析：考查虚拟语气的用法。句意为“他们本该午饭时到达，但他们的航班推迟了。”will have done将来可以完成；can have done可能做过……吗？表示对过去行为的怀疑，用于疑问句；must have done一定做过某事，表示对过去事情的肯定推测；should have done本来应该做某事，而实际没做。but their flight was delayed这样的结果，说明他们本来该到达却没有到达，因此选D。
2.(2011全国卷II,8) If you smoke, please go outside.
A. can B. should C. must D. may
答案 C
解析：考查情态动词的用法。句意为“如果你非得要抽烟，请到外面去抽。”must (表示主张)一定要，坚持要。根据后一句please go outside的要求，选C。
