用关系代词that,which,who连接句子

1、Mike bought a camera that was made in Japan.
2、The boy which I know is very nice.
3、I know the girl who is going out with my cousin.
4、The shoes that my grandma bought are too big
5、You are sitting on a bench on which the paint is still wet.
再问： 第2题的 The boy不是人吗？为什么用which
再答： 用who也行，that 也行；which 的话没有前两个好，你还是用前两个吧。