First Q is from GmatPrep and the second Q is from Gmat Paper Test Code 42. How come B is incorrect in Q1, but similar rules (for 'it') seem to work fine for Q2.

Q1. 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
OA is C, Why not B or D.

[second question redacted - NOTE TO POSTER: the ets paper tests, in addition to being rather outdated, are also banned sources on this forum]

so it appears that you've correctly eliminated (a) and (e), because 'than' doesn't go with 'ten times as much [as]'.

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both (b) and (d) suffer from the improper use of the pronoun 'it'. the poor usage is extremely well camouflaged, though: not only is there a lot of 'junk' between the two halves of the construction, but one half is in the underlined part and the other half is in the non-underlined part.

as an analogy, consider the (equally incorrect) usage of 'they' in the following:
more than twice as many immigrants live in our city as they did in 1980.
this doesn't make any sense, because there is no proper referent for they: this pronoun would have to refer to a specific set of people, the only candidate being the 'twice as many immigrants' (which makes no sense, as they can't be more than twice as many as themselves). you are not allowed to cherry-pick 'immigrants' out from under the cover of 'twice as many'.**

same issues apply to the problem at hand.

**this is a general truth: you can't use a pronoun to refer to an existing noun without the adjective(s) attached to that noun. so, for instance, you can't say
blue ferraris look just as good as they do in red, because then you're saying the cars are simultaneously red and blue,
but you could say
ferraris look just as good in blue as they do in red.