）she went out of the room ,she turned back and knocked at th

）she went out of the room ,she turned back and knocked at the teacher's door agai
请问各位懂英语的两道题.1. （ ）she went out of the room ,she turned back and knocked at the teacher's door again.这一句为什么开头要用Before而不是As soon as呢?好奇怪2. The exercise is so difficult that few of us can do (it). 为什么这个it不能省略呢?

Before 是在.之前的意思,as soon as 是一.就的意思,你把意思放到句子里,明显as soon as 的意思不符合的.2.so...that 这是一个句型,表 太.以至于.这里的it 一定要加上去,是特指前面的exercise.但是如果换个形式就可以不加it ,The exercise that few of us can do is so difficult.这是个定语从句,that 指代前面的exercise,倒过来就成为,few of us can do the exercise,所以这里就不用加it了.这个句子可以拆成2个小短句 The exercise is so fifficult,few of us can do the exercise.
没明白可以继续问我