由时间状语来判定
一般说来,各种时态都有特定的时间状语。与过去完成时连用的时间状语有:
( 1 ) by + 过去的时间点。
如: I had finished reading the novel by nine oclock last night.
( 2 ) by the end of + 过去的时间点。
如: We had learned over two thousand English words by the end of last term.
( 3 ) before + 过去的时间点。
如: They had planted six hundred trees before last Wednesday.
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