现在完成时（非延续性动词）与过去完成时都发生在过去，要如何区别

现在完成时（非延续性动词）往往出现在一些特殊的语言环境中，这时的完成是类似于汉语中的“刚才”

在某些疑问句中表示很近的过去：
Where have you been?
What have you done?

这种过去往往是没有时间状语的，如果句中出现just now这样的时间状语，那就还用过去时，即使要表达的意思完全相同

一般过去时一般都需要时间状语

现在完成时用非持续性动词还可以是句子为否定句的情况

I haven't finished my homework yet.

下面是这两种时态的用法总结：

现在完成时：

用法：

（1）表示已经完成的动作

（2）延续至今的动作，常与for、since等连用：
We have been good friends since our middle school days.
We have studied English for six years.

（3）用在条件或时间状语从句中，表示将来某个时间之前已经完成的动作：
He will come as soon as he has finished the homework.
If you have read the book before I leave, please lend it to me.
We shall wait here until the rain has stopped.
Won’t get off the bus until it has stopped.

（4）某些疑问句中表示很近的过去：
Where have you been?
What have you done?

（5）先行词用序数词修饰的定语从句：
It is the first time that I have been to the Great Wall.

注意：

（1）与某些副词连用：already、just、yet

（2）一般不能有时间状语

（3）可以与表示从过去延续至今并包括现在在内的一段时间的状语连用，如today、this morning、recently、in the past few years、since then：
Their condition have improved recently.
Have you been to the museum this morning?
现在完成时和一般过去时的区别：
We have visited a power station.
We visited a power station last week.

一般过去时：

表示在过去某一点时间发生的动作或所处的状态：
He arrived in Beijing an hour ago.
Where were you just now?
有明显的表示过去的时间状语

表示过去反复出现的动作：
Their children often went hungry in the old days.
频率副词也可以用一般过去时
除此之外，used to、would也可以表示过去常常做的是：
I used to go to work at seven o’ clock.
What time did you used to get up last year?
Whenever I had a chance, I would go to Wang’s to have a talk with him.
其中used to do的否定形式有两种：didn’t used to do 或usedn’t to do

有些具有现在意义的时间状语需要用过去时态，如today、this week、this month等：
I saw him today.
He came late three times this week.

额...我们老师说过，过去完成时就是发生在过去的过去，现在完成时就是从过去持续到现在基本上都有一些时间标志的词