一、过去完成时
形式:
had + done
解释：
过去的之前(全部完成/部分完成)
二、过去完成时 变否定疑问
She had left.
She had not left.
Had she left?
What had she done?
三、过去完成时 与一般过去时的搭配使用
When he got there, she had left.
一般过去时 过去完成时
过去 过去的之前
He finished work. He went home. (after)
After he finished work, he went home.
After he had finished work, he went home.
He went home, after he had finished work.
四、过去完成时 vs 现在完成时，过去完成时 vs 一般过去时 vs 过去将来时
下面是帮助理解：
过去完成时，站在过去看之前，已经完成
现在完成时，站在现在看之前，未必完成
一般过去时，过去发生的
一般现在时，现在经常
现在进行时，现在正在做
一般将来时，未来可能发生的
一般将来进行时，未来一定发生
The plane was late ...A few hours earlier, someone had told the police that thieves would try to steal the diamonds.On Wednesday evening, we went to the Town Hall.... a large crowd of people had gathered under the Town Hall clock. It would strike twelve in twenty minutes’ time.
