关于定语从句 whom的用法.

关于定语从句 whom的用法.
① whom的用法是什么？
This is the house in which Lu Xun once lived。（原句，我不懂什么时候要加介词 我什么时候知道要加 什么时候不加）
为什么上面的例句不能是：This is the house which/that Lu Xun once lived in
② Do you like the book on which she spend dollar 10？
I will never forget the day which we spent together。
（这里为什么一个有介词on 一个不用介词。）
③ I don't like the way that you speak to your parents。
We don't understand the way that/whichi he told us。
（不是说先行词是the way 或者in the way要用 that ）