修饰门的,还原到最后面怎么还原回去？谁的后面？It happened that father had sent us upstairs because he thought he would be able to lock the door-which was twenty feet away-before the animal reached it 这就是正确的句子刚好你亲己经把我们送到楼上了，因父亲认为他能在那个动物到达前关掉这个门（这个门离他20英尺远）两个横线是破折号，插入which was twenty feet away来说明door去掉这个插入语句不影响原句结构