Pronouns that dont need a reference?

[Vizay]

Students in the metropolitan school district lack math skills to such a large degree as to make it difficult to absorb them into a city economy becoming ever more dependent on information-based industries.

(A) lack math skills to such a large degree as to make it difficult to absorb them into a city economy

becoming

(B) lack math skills to a large enough degree that they will be difficult to absorb into a city's economy that becomes

(C) lack of math skills is so large as to be difficult to absorb them into a city's economy that becomes

(D) are lacking so much in math skills as to be difficult to absorb into a city's economy becoming

(E) are so lacking in math skills that it will be difficult to absorb them into a city economy becoming

Source: OG 11th edition..

This question was discussed earlier, but some points were left unanswered. So I want to ask the question again.

The correct answer here is E. But during my elimination process, I removed E as it contained a pronoun 'it' that didnt refer to anything. So I am confused on how it can be the correct answer. I see explanations that E has the correct idiomatic usage. So if that is the case, does the pronoun error have a lesser priority than idiomatic error? I have also seen few other sentences where pronouns like it and there are used without a clear antecedent, but are still correct.

Please clarify the answer. (I am taking the test in 3 days, any explanation would be appreciated)

Thanks
Vizay

[RonPurewal]

this 'it' is a well-established nuance of english grammar, certainly familiar to you if you've spoken and written enough english to compose a post such as the one here.

consider:
it is important that you be on time.
it's unbelievable that those things sell for so high a price.

in each of these sentences, 'it' stands in for the following noun clause (that you be on time, that these things sell for so high a price). yes, this theoretically makes the construction somewhat redundant, but that's the way it works.

in general, the construction is
it is ADJ for NOUN INFINITIVE
or
it is ADJ that NOUN CLAUSE
there are probably other versions, but i believe those are the two most common.