先把句子还原.We stay together in Beijing last summer.这里stay together之间并没有in.（in Beijing 不算,这in修饰地方的）但是我说Do you syill remember the school where we study together?这里还原就是we study in the school together.注意这句study 与the school之间有in,所以可以用说成Do you syill remember the school in which we study together?试比较这2句.
你初三的吧~..