正误辨别，仔细体会：This is the room where I once lived. （正）This is the room I once lived in.（正）This is the room which I once lived in.（正）This is the room that I once lived in.（正）This is the room in which I once lived.（正）This is the room where I once lived in. （误）第一个为什么对，最后一个为什么错，不是很清楚了吗？