Hello Everyone!
Let's tackle this question, one problem at a time, and narrow it down to the correct answer! First, here is the original question with any major differences between the options highlighted in orange:
In 2000, a mere two dozen products accounted for half the increase in spending on prescription drugs, a phenomenon that is explained not just because of more expensive drugs but by the fact that doctors are writing many more prescriptions for higher-cost drugs.
(A) a phenomenon that is explained not just because of more expensive drugs but by the fact that doctors are writing
(B) a phenomenon that is explained not just by the fact that drugs are becoming more expensive but also by the fact that doctors are writing
(C) a phenomenon occurring not just because of drugs that are becoming more expensive but because of doctors having also written
(D) which occurred not just because drugs are becoming more expensive but doctors are also writing
(E) which occurred not just because of more expensive drugs but because doctors have also written
While there are a lot of differences between the options, there are a couple glaring differences we can focus on to start:
1. not just... / but... (Idioms)
2. are writing / having also written / are also writing / have also written (Verb Tense & Meaning)
Let's start with #1 on our list: idiom structure. Here is a quick breakdown of the idiom we're using here, and which forms of it are acceptable:
not just X, but also Y = GOOD
not just X, but Y = GOOD
Remember that in any idiom that includes X and Y, they both MUST use parallel structure! Let's take a closer look at each option, and rule out any that don't use the idiom or parallelism correctly:
(A) a phenomenon that is explained not just because of more expensive drugs but by the fact that doctors are writing --> NOT PARALLEL
(B) a phenomenon that is explained not just by the fact that drugs are becoming more expensive but also by the fact that doctors are writing --> PARALLEL
(C) a phenomenon occurring not just because of drugs that are becoming more expensive but because of doctors having also written --> PARALLEL
(D) which occurred not just because drugs are becoming more expensive but doctors are also writing --> NOT PARALLEL
(E) which occurred not just because of more expensive drugs but because doctors have also written --> NOT PARALLEL
We can eliminate options A, D, & E because they don't use parallel structure within the idiom we're using here.
Now that we've narrowed it down to only 2 options, let's tackle #2 on our list: verb tense & meaning. Read over each option carefully, and make sure that the meaning is clear and logical:
(B) a phenomenon that is explained not just by the fact that drugs are becoming more expensive but also by the fact that doctors are writing
This is CORRECT! The idiom "not just X, but also Y" is used correctly and has parallel structure throughout. The verb "are writing" is also clear and makes sense here logically.
(C) a phenomenon occurring not just because of drugs that are becoming more expensive but because of doctors having also written
This is INCORRECT. While the idiom is used correctly, and it uses parallel structure, there's a problem with the verb at the end. By adding in the word "also," the sentence now suggests that the doctors did more than one thing - but we don't know what the other thing is! WHAT did they do in addition to writing prescriptions? It's unclear, so let's rule this out because it's not logical to say doctors "also" did something when we only see one action in the sentence.
There you have it - option B is the correct choice! By focusing on the simple, yet obvious differences first, we were able to narrow down our options significantly to make the process go quickly!
Don't study for the GMAT. Train for it.
