I remember this question in the past when I faced it in the SC1000. I chose this one because choice B and D, "it" refer to no antecedent. After that, I also found in manhattan forum that contain this problem. Here is the topic discussing about this problem and Ron Purewal's explanation:
i could've sworn this problem was in another thread, but the search box won't find it. http://www.manhattangmat.com/forums/the ... t3322.html
there are two splits you should use to narrow down this problem:
(1) the second half of the construction 'ten times as much ... ____' is as, not than. therefore, you can eliminate answers (a) and (e), which contain 'than'. (i'm assuming that (e) is supposed to say 'than', not 'then'; i don't think the gmat problems would that blatant an error)
(2) the pronoun 'it' is inappropriate, because 'it' must refer to the ENTIRETY of the noun phrase serving as an antecedent.
for instance, the following is an improper sentence: last year's attendance was ten thousand greater than it was this year
in the above sentence, the pronoun 'it' must necessarily refer to last year's attendance, not just attendance.
the problem in this post has the same issue: the pronoun 'it' must refer to more than ten times as much energy, not just energy - an interpretation that makes no logical sense. therefore, all answer choices containing the pronoun 'it' are wrong.
if you don't like '...than was the case', you should learn to like it; this is one of those phrases that the gmat writers use to refer to concepts that don't fit under the usage constraints of traditional pronouns. (another popular one of these constructions is 'do so'.)
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