过去完成时（1）常用过去完成时的几种情况：①by, by the end, by the time, until, before, since后接表示过去某一时刻的短语或从句。By the end of last year, we had produced 20,000 cars.The train had left before we reached the station.②表示未曾实现的希望、打算、意图、诺言等。常用had hoped/ planned/ meant/ intended/ thought/ wanted/ expected等或用上述动词过去式接不定式完成式表示，即had hoped/ planned/ meant/ intended/ thought/ wanted/ expected to have done。③“时间名词＋before”在句子中作状语，谓语动词用过去完成时；“时间名词＋ago”在句子中状语，谓语动词用一般过去式。He said his first teacher had died at least 10 years before.Xiao Hua left school 3 years ago.④表示“一……就……”的几个句型：Hardly/ No sooner/ Scarcely had ＋主语＋过去分词＋when/ than/ before＋一般过去时。We had no sooner been seated than the bus started. = No sooner had we been seated than the bus started.（2）在before或after引导的时间状语从句中可用一般过去时代替过去完成时。After he (had) left the room, the boss came in.We arrived home before it snowed.
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