我的问题：我不明白为什么句子1,2,5,6 是对的，3,4 是错的。 判断改错
1.（对）This is the mountain village where I stayed last year.
2.（对）Ill never forget the days when I worked together with you.
3.（错）This is the mountain village where I visited last year.
4.（错）I will never forget the days when I spent in the countryside.
5.（对）This is the mountain village (which) I visited last year.
6.（对）Ill never forget the days (which) I spent in the countryside.
如题
