在看新东方笔记的时候，看到“比较级中前句所提的部分在后面比较结构中可以用THAT，THOSE代替”，那IT可以用吗

177.Bihar is India’s poorest state, with an annual per capita income of $111, lower than in the most impoverished countries of the world.
(A) lower than in
(B) lower than that of
(C) and lower than that of
(D) which is lower than in
(E) which is lower than it is in
the key: B
比较考点：比较对象

这里的THAT所指的是an annual per capita income 吗，可否用IT来代替，E答案为什么错呢

相比较

299.Florida will gain another quarter-million jobs this year alone, many of them in high-paying fields like electronics and banking, making the state’s economy far more diversified than ten years ago.
(A) high-paying fields like electronics and banking, making the state’s economy far more diversified than
(B) high-paying fields like electronics and banking, and making the state’s economy far more diversified than its economy
(C) high-paying fields such as electronics and banking, to make the state’s economy far more diversified than
(D) such high-paying fields as electronics and banking, making the state’s economy far more diversified than it was
(E) such high-paying fields as electronics and banking, and make the state’s economy far more diversified than it was
the key
比较考点:比较对象。
the state's economy is far more diversified than it was ten years ago

这里的the state's economy 可以用THAT代替吗，变成than that was ten years ago?

关于it,that的用法现在有点糊涂，是不是在做主语时候的指代用IT，其他情况下用THAT或者THOSE呢。。。麻烦大家解惑。。。

个人理解

一般it可以单独用，that those要有限定成分，，that of。。。之类的

可能不对啊，我刚看了一个星期GMAT

“比较结构的后半段，相同的名词为了避免重复，用代词that/those来指代”。但好象没有看到关于IT的用法的解释。

在177题中E错在哪呢。而在299题中，than it was可以变成than that was吗。。。求解答。万谢