首先纠正一下,we drive to work is always crowded 不是从句,确切的说是后面的 is always crowded 是主句.拼写有误应该是expressway
the expressway (on which ) we drive to work is always crowded
在这里the expressway 是整个句子的主语,is是系动词 crowded是 表语,因为always是副词所以可以修饰crowded,译为一直很拥挤,或者总是很拥挤.on which we drive to work 是定语从句修饰主语 expressway.如果把on which 放回从句应该是we drive on which (the expressway) to work.在路上开车当然要用on 了 .总不能在路里面开车吧.