點分Who同Whom？

who同whom 都是指 "誰"
(whose才是 "誰的")

兩者的分別是：
1. who is used as the subject(主語) of the sentence/clause
The old man who live next door is 70 years old. (主語是the old man)

2. whom is used as the object(賓語) of the sentence/clause
The boy whom we met is Susan's brother. (object賓語是the boy)

不過，現在很多時我們都唔會再分who/whom 。 我們大多數用who，意思是who可以取代whom，不用再細分了。

2. past perfect and present perfect

1. present perfect (have/has + p.p) 是以前發生的事對現在還有影響力
I have known her for 3 years. (你現在還認識她)
She has learnt to play the piano since 2001.(由01年到現在還學琴，顯示持續性)

2. past perfect (had + p.p) 要同past tense一齊用，目的是顯示過去所發生的事情之先後次序：
After she had taken a shower, she started to do her homework.
I didnt see him. He had left when I arrived.

past perfect用以強調past actions既先後次序，所以較少用。