Today's technology allows manufacturers to makes small cars more fuel-efficient now than at any time in their production history.

a)
b) small cars that are more fuel-efficient than they were at any time in their
c) small cars that are more fuel-efficient than those at any other time in
d) more fuel-efficient small cars than those at any other time in their
e) more fuel-efficient small cars now than at any time in

Can you please explain why C is correct and why B is incorrect? Would B be correct if it did not have 'their' at the end? I just don't get this question. Thanks.

I'm going to assume that, when you typed "makes" above in the non-underlined portion, that was a typo? It should say "make"?

Yep Pronouns must have one, clear, unambiguous antecedent. Does their refer to manufacturers? Small cars? Clearly, I want it to refer to small cars (logically), but it could refer to manufacturers. Need to make this clear (which C does by just removing it from the equation).

It's also important to use the word "other" - technically, they're not more efficient than those at ANY time in production history - because part of the at history includes right now, when they're more fuel-efficient. So, they're only more efficient that those at any OTHER time in history.

Thanks for the explanation Stacey. I have one further question though; doesn't 'their' in Choice B clearly and unambiguously refer to the noun that immediately precedes it (as it should), which is 'cars'?

I guess I'm trying to understand whether we can 'assume' that 'their' refers to 'cars' on this and other such GMAT questions since a pronoun usually refers to the noun immediately preceding it.

Thanks.

nooooooo no no no. that's a sure route to disasterville, or, at the very least, a way to make problems harder than they need to be.

the gmat is very big on the idea of completely unambiguous pronouns. in other words, ideal answer choices have pronouns that have only one possible antecedent - not just one antecedent that passes the common sense test, but one antecedent, period. you should follow this rule religiously, eliminating any answer choices in which pronouns could technically refer to more than one noun - even if all but one of said nouns are absurd.

sometimes, but very rarely, the gmat will feature a problem on which a pronoun technically has multiple antecedents in all choices (thus forcing you to 'eliminate' everything). only in those cases should you apply your 'common sense' to determine which pronoun is the true antecedent. again, this rarely ever happens, so make sure that your primary attitude is 'one possible antecedent or bust'.

in the problem referenced here, 'they' could technically refer either to the cars or to the manufacturers (even though the latter is totally illogical), rendering that choice incorrect.

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final comment: sometimes pronouns distinctly (and correctly) refer to nouns that don't directly precede them - most notably in cases when the directly preceding noun doesn't agree in case/number/etc. for instance:
stephanie needs to sell eight more tickets to fufill her quota.
here, the noun directly preceding 'her' is tickets, but 'her' must refer to Stephanie. pardon me if this is obvious, but note that it proves the 'directly preceding noun rule' to be a non-rule.

Fabulous! Thanks for the explanation.