In English, Tense的分別?

1.我已改了密碼.
Past Tenses 是動作和事情是過去發生並且過去完成，不會持續到現在。

2. 這句句子是錯誤的.
應該說" I have changed the password already"
當強調一個動作我們做了多少次或發生次數，我們會用 Present Perfect Tense

3. 這個也是錯的.
可以說" I had changed the password before you arrived."
Past Perfect Tense 不需要像 Present Perfect Tense 般注意什麼 "有沒有準確時間"，只要在相比下較 Simple Past Tense 早，便可以交給它去辦了。

希望幫到你.^^

1. simple past, 直接講過去左既事。
-I changed the password,指轉左密碼﹐總之係轉左。

2. present perfect, 一d過去左既野但時間上仲有同而家講緊呢一刻有關連。
-I have changed the password, 指已經轉左密碼﹐ 直至以家呢一刻已經轉左。

3. past perfect, 一d過去左既野但係同而家講緊呢一刻既時間上完全無關連。
-I had changed the password, 都係指已經轉左﹐ 但係指之前已經轉左。

arm arm 睇完答題一號﹐ 他說2﹐3﹐ 也是錯﹐
其實是他自己錯....

1. I changed the password (pw)
You changed the pw in the past. This action has no effect to the present.

2. I have changed the pw
You have changed the pw, so something is affected by this action now. It means this action is still valid.

3. I had changed the pw (....)
You had changed the pw before something happened in the past. So it only affected something in the past. You use Past Perfect Tense to indicate an action happened before another action in the past. Hence, this sentence is incomplete.

Is it simple to understand??