請問以下3句英文句子的分別

你好，这三句明显是有很大的分别，就让我慢慢地解释给你看咯。

I have finished my work. (Present Perfect Tense)
我已经完成了或做完了我的工作或功课等。

Present Perfect Tense是用在我们讲述着一个我们不知道时间而又是现在之前发生的过去动作(an action happened at an unspecified time before now)。

I had finished my work. (Past Perfect Tense)
我已经完成了或做完了我的工作或功课等。

你是否发现我这个解释跟上一个是完全一样的吗？可能你也会怀疑我有没有写错呢？
其实当我们要用Past Perfect Tense时，我们最好是用在某样事情或某个动作在另一个过去了的动作之前，也就是something happened before another action in the past。
所以啊，我觉得你以上的这个句子可能是不够完整的。

I finished my work. (Past Tense)
我完成了或做完了我的工作或功课等。

Past Tense主要是说着一个在特定的或明确的过去时间里开始了和停止了的动作，也就是说an action started and finished at a specific time in the past，简单的说就是completed action in the past。
但我们也不需要真的注明那个明确的时间，就好像你所发问的句子一样咯。

以下是我另外加给你看的，那些都是有关Present Perfect Tense的句子。

Unspecified Time Before Now:-
1) I have been to Malaysia.

Time Expressions with Present Perfect:-
2) I haven't seen Alex for two days.

Duration From The Past Until Now:-
3) I haven't seen Alex since Monday. (= from Monday until now)

希望能帮到你咯。。。: )

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第一句的時態是現在；一般的說法是「現在完成式」的運用；是用以表達現在的事態。
第一句就解作「我已把工作完成了。」以現在看，工作何時完成？那不是重點所在；重點在工作的現時狀況：是剛開始？已完成一半？還是已完成呢？如果想知道工作何時完成，一般來說，你是要用過去的時態發問：When did you finish your work?了。
第二句不常見。但在故事的敘述中，因以整體為「過去式」，故也有用作現在完成式的代入，尤以美式英語為常見！
第三句是簡單過去式的運用！你就可以名正言順地問：When did you finish your work?了。

I have finished my work. (YOU ANSWERED THE QUESTION when being asked by somebody - Have you finished your work?)

You have finished your work by this time (no definite time indicated)

I had finished my work.= IT NORMALLY DOES NOT STAND ALONE. SEE EXAMPLE BELOW & IT HAPPENED IN THE PAST.

I had finished my work before you returned home (Normally we answered the question, when did you finished your work?)


I finished my work.(LAST WEEK /YESTERDAY/ LAST NIGHT ETC) Did you finish your work last week? or during essay writing .