A who，whom
在正规英语中我们用介词+whom结构：
With whom did you go?
你和谁一起去的?
To whom were you speaking?
你刚才在跟谁说话?
但在日常口语中我们常把介词置于句末。这时一般将whom变成who：
Who did you go with?
Who were you speaking to?
B which，what
在正规英语中我们用介词+which/what结构：
To which address did you send it?
你把东西寄到哪个地址去了?
On what do you base your theory?
你的理论依据是什么?
在非正规英语中我们将介词置于句末：
Which address did you send it to?
What do you base your theory on?