求教在比较题和形式主语中it的指代问题

本帖最后由 supermanlee 于 2011-2-18 21:26 编辑

在比较题中 it 好像常因指代不明列为错误选项
在这里列出两个例子提出问题期待nn解答～

prep2007 sc2 96.(29547-!-item-!-188;#058&004302)
There are hopeful signs that we are shifting away from our heavy reliance on fossil fuels:more than ten times as much energy is generated through wind power now than it was in 1990.
(A) generated through wind power now than it was
(B) generated through wind power now as it was
(C) generated through wind power now as was the case
(D) now generated through wind power as it was
(E) now generated through wind power than was the case
正确答案为C          给出的分析是首先as...as...排除AE
BCD中因为it 会在这里指代the energy genertated through wind power now n从而产生歧义选C

大全168
Because the Earth’s crust is more solid there and thus better able to transmit shock waves, an earthquake of a given magnitude typically devastates an area 100 times greater in the eastern United States than it does in the West.
(A) of a given magnitude typically devastates an area 100 times greater in the eastern United States than it does in the West
(B) of a given magnitude will typically devastate 100 times the area if it occurs in the eastern United States instead of the West
(C) will typically devastate 100 times the area in the eastern United States than one of the comparable magnitude occurring in the West
(D) in the eastern United States will typically devastate an area 100 times greater than will a quake of comparable magnitude occurring in the West
(E) that occurs in the eastern United States will typically devastate 100 times more area than if it occurred with comparable magnitude in the West
正确答案为
给出的思路是it 在这里指代 the earthquake of a given magnitude that dvastates an aera in the eastern US
自然不能是在和西边的earthquake项比较

看了这两个例子之后对it出现在比较中很是警惕

在形式主语中很经典的用法是 it takes sb. some time to do sth
在不定式做修饰中有 to do 后不接宾语
如果上述句型中to do 理解为some time的修饰是否可以？
那形式主语中的it 指代的是整个to do sth还是 sth？

请教nn～ it 的指代用法到底是怎样的？
期待nn指正上述思路中的错误之处

谢谢～