我想問perfect tenses 點用??

Perfect tenses:
1. Present perfect tense
2. Past perfect tense
usage:
1. a. 當說及一些事件發生於以前，並繼續進行至現在
e.g. I Have lived/have been living in this house for years／since 1992.
b. 當強調一個動作我們做了多少次或發生次數
e.g. He has broken his arm four times before.
c. 我們會用 Present Perfect Tense 來表達一個較長久，永恆的事情。
2. a. used for a past action that happened before another past ascion
e.g. Mr. Leung had knocked the door before he left home yeserday
b. used for an acyion which ended before a point of time in the past
e.g. By 9:30 a.m., the postman had already collected the letters.

以 Present Perfect Continuous Tense 來表達一個比較臨時，較短暫的動作
當一個動作於過去發生，持續到現在，並有可能會繼續發生至將來
e.g. You have been working hard recently. You should take care of your health.

Perfect tens 分別有
-Present perfect tens 現在完成
-Past perfect tens 過去完成
-future perfect tens 將來完成

對了 ! Persent perfect , 凡表示過去動作, 到現在已完成或還在續 , 須用present perfect
e.g.I have studied English for five years. 我英文讀了五年了

而past perfect continuous tens 過去完成進行 , 表示過去的動作在"過去某一動作發生時, 還在繼續行動.

e.g. He had been living in Tainan before he moved.
在他搬到此地以前, 他一直住在台南

I had been waiting for more than an hour when he came.
他來的時候, 我已經等了一個多小時了。