15 过去完成时

语法结构：had +过去分词
I /we /they /you/ he /she /it + had + gone/seen/finished
表示事情或动作发生在过去的过去：
When Sarah arrived at the party, Paul had already gone home.

When we got home last night, we found that somebody had broken into the flat.
Karen didn't want to come to the cinema with us because she had already seen the film.
At first I thought I'd done the right thing but I soon realized that I had made a serious mistake.
The man sitting next to me on the plane was very nervou. He hadn't flown before./He had never flown before.
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比较过去完成时和一般过去时:
Was tom at the party when you arrived?
No, he had already gone home.
Was tom there when you arrived?
Yes, but he went home soon afterwards.
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Ann wasn't at home when I phoned. She was in London. Ann had just got home when I phoned. She had been in London.