区别定语从句which和where

区别定语从句which和where
1.he found a place_________he used as his office.
a.where b.which
2.the factory _______ we visited is a large one.
a.where b.which
3.the factory _______we visited its modern shops is a large one.
a.where b.which
详细的讲下区别吧～看过其他的回答,但是没懂怎么样区别是却宾语还是缺状语.
有人答案都是错的，还说人家不懂什么什么的，好笑