it is the tallest tree that i have ever seen定语从句中如果先行词有最高级或比较级修饰,关系代词只能用that
this is the school where/in which he sdudied 没有in that的说法,也就是说用了that就前面不能加介词,这里school在从句中作地点状语,所以用where引导,又因为是study in the school,所以也可以用in which