过去将来时 形式类似于 would + do 1,would 更兼具情态动词用法: I knew you would agree. 我知道你会同意的。 2,在虚拟语气中使用: If I were you,I would go at once.如果我是你,我马上就会去。至于你给的例句,完全不需要用过去将来时: Tomorrow when they open the door they will notice immediately that something big has happened here since last night. 你硬要用也不是不可以: They did a big thing last night which would be noticed immediately tomorrow when they open the door 原则是主从句时态保持一致
原句是真实条件句,相当于还没有发生的将来时态。语法规定主将从现。可以理解成,将来他要是在这所学校学习,他就会熟悉你。(这是真实情况)
如果改为虚拟语气,则表示的是与现在相反的情况。可以理解成 他现在没有在这所学校学习,他对你不熟悉。