给你推荐一个网址，特全，很好用。
这还是当初我们学的时候，老师给的。
http://www.kekenet.com/nce/42919.shtml
要哪一部分的？
A detectives were waiting（1.1）; They were expecting(1.2) ; detectives were waiting(1.5) ； others were waiting (1.6) ; two detectives were keeping guard(11.7-8)
个人建议你去买一本叫《新概念英语-练习详解》的书（分1-4册）小本的，很详细
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