现在完成时和过去完成时的用法谁能告诉我什么是现在完成时?什么是过去完成时?在什么情况下用?该如何用?

现在完成时have done 的时间标志是
in the past few/three years
since + 时间点/ sb dis
副词标志是
already,yet,never,ever
现在完成时可以单独使用
i have finished homework.
但过去完成时不可以单独使用
用在“It is the first/second...time+that”从句中
过去完成时 had done
时间标志
by last year/by the time of
过去完成时一般和过去时一起出现
sb had done sth before sb did
sb did sth after sb had done
用于hardly when,no sooner than的句式中
we had hardly came home when it rained.
用在“It was the first/second...time+that”句型中

现在完成时:havehas done
1.表示在说话之前已经完成的事态
2.表示从过去某一时刻开始，持续到现在的动作或状态
3.用在从句中，表示一个动作先于另一个动作
4.用在“It's the first/second...time+that”从句中
过去完成时:had done
1.表示在过去某一时间活动作之前已发生的动作或情况
2.表...