现在完成时:have + 过去分词， 表示过去发生的动作对现在造成的影响或结果。
过去完成时：had +过去分词，表示过去的过去已经完成或发生的动作。如
He has finished his homework.
The train had left when he got to the station .
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追问缩写是不是直接在人称后加" 've "？
追答是的，‘ve / 's
He's finished ...= He has finished...
They 've finished .... = They have finished ...