在学习英语语法时，过去完成时可能是最难理解的时态之一。它用于描述在过去某个时间点之前已经完成的动作。为了更好地理解这个时态，我们需要掌握一些标志词，这些词语可以帮助我们判断何时应该使用过去完成时。
以下是16个常见的过去完成时标志词：
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By the time 例如：By the time we arrived at the party, the cake had already been eaten.
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Before 例如：I had finished my homework before my parents came home.
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After 例如：I was exhausted after I had been running for an hour.
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When 例如：When I got to the cinema, the movie had already started.
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As soon as 例如：As soon as I had finished my breakfast, I went for a walk.
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Just 例如：I had just finished my dinner when the phone rang.
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Already 例如：I had already seen that movie, so I didn't want to watch it again.
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Yet 例如：He had not yet received the email when he left the office.
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Since 例如：I had not seen my old friend since we graduated from college.
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For 例如：I had been waiting for the bus for over an hour when it finally arrived.
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Up until 例如：Up until that point, I had never tried sushi.
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Hadn't realized 例如：I hadn't realized how much time had passed until I looked at the clock.
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Hadn't expected 例如：I hadn't expected to see so many people at the party.
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Hadn't known 例如：I hadn't known that she was afraid of heights until we went on the Ferris wheel.
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Hadn't heard 例如：I hadn't heard the news until my friend told me about it.
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Hadn't seen 例如：I hadn't seen my sister for years before she came to visit me.
掌握这些标志词可以帮助我们更好地理解过去完成时的用法，从而更自如地运用这个时态。希望这篇文章能对你的英语学习有所帮助。
