DmitryFarberHi,
Would option A] and B] be correct, had we replaced 'them' with the correct noun. Does 'IT' after 'BUT' in option B] creates a problem because otherwise the meaning would be correct.
By offering lower prices and a menu of personal communications options, such as caller identification and voice mail, the new telecommunications company has not only captured customers from other phone companies but also forced them to offer competitive prices.
(A) has not only captured customers from other phone companies but also forced them
(B) has not only captured customers from other phone companies, but it also forced them
DmitryFarber wrote:
There is no absolute rule for identifying the antecedent. "Them" can refer to any plural noun in the sentence, as long as "they," "them," or "their" hasn't already been used to refer to some other plural noun. However, it's important to use sentence structure and whatever you can gather of the author's intent to determine the correct antecedent. The GMAT doesn't test pronoun ambiguity much, but since we have a choice in this case to replace the unclear "them" with the actual noun, it's wise to do so.
As for the word but, it does not necessarily require a comma. You definitely use a comma if it's joining two independent clauses:
I'm enjoying the party, but I have to leave now.
However, there are many other cases where we don't need one:
The robot has a small but powerful engine.
All but one of the guests arrived late.
I aced the verbal section but timed out on the quant.
Or, as we see here . ..
She has not only written three bestselling novels but also developed fifteen important patents.
Note that the use of "has not only" vs. "not only has" cannot be decided in isolation. Either construction could work. "Not only . . . but also" is a parallelism indicator, so we can use "has" afterward as long as it is parallel. In other words, we can say "She has not only X but also Y" or "She not only HAS X but also HAS Y." We just can't say "She not only HAS X but also Y." Having said that, I prefer the usage in the correct answer. There's not much reason to use "has" twice.