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？