Which hotel did you stay in?Where did you stay?为什么第二句不用加in啊

因为 which 是代词,而stay是不及物动词,不能直接带宾语,要借助于介词in才能带宾语：stay in which
而where 是副词,可以直接修饰动词,不需要介词的帮助：stay where