请问IT 在考试是不是一定要所具体指代的对象, 不可能出现形式主语的情况?以下这俩个句子中, IT的作用又有什么不同呢?

1. Although just inside the orbit of Jupiter, amateur astronomers with good telescopes should be able to see the comet within the next few weeks.

(A) Although just inside the orbit of

(B) Although it is just inside the orbit of

(C) Just inside the orbit of

(D) Orbiting just inside

(E) Having orbited just inside

2. Although aspirin irritates the stomach, it can be avoided if the aspirin tablet is given a coating that will not dissolve until the tablet reaches the intestine.

(A) Although aspirin irritates the stomach, it

(B) The irritation of the stomach caused by aspirin

(C) The fact that aspirin causes irritation of the stomach

(D) Aspirin causes stomach irritation, although it

(E) Aspirin irritates the stomach, which

it 可以充当形式主语或形式宾语。

第一题选B，it指代comet，虽然XDF的老师说it出现在主句前，优先指代主句主

语，但这里主语为astronomers，明显it不能指代astronomers，所以it指代

comet，所以这里用it不会产生歧义。

至于第二题，it不能指代前面的整句话（这条规律绝 对正确），所以可以排除选项A。D中的IT从语法角度看指代Aspirin。

请指教