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 o'clock 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.