定语从句中什么时候只能用where不能用that

当定语从句中缺少地点状语时,关系词只能用where,而不能使用that.
当定语从句缺少表示地点的主语/宾语而不是地点状语时,关系词使用that/which,而不使用where.
如：This is the city where I stayed last year.
定语从句I stayed last year缺少地点状语,用where = in which = in the city.
= This is the city that I stayed in last year.
定语从句I stayed in last year中,in后面缺少宾语,用that,不用where.