You might be reading too far into this one. There is the conditional issue, but there are other grammatical issues at play here that help eliminate wrong answer choices.

In D, "ability for broadening" is not idiomatically correct. The correct preposition to pair with ability is "to", as in "I have the ability to ace the GMAT." This issue eliminates D & E right off the bat.

It's important to note here that saying "I can ace the GMAT" is preferred to "I have the ability to ace the GMAT" since the "can" construction is more direct and concise. Note that in the correct answer, the form switches to the preferred "can" form. This, in my mind, is the real issue at play between A/B and D/E.

But we should always eliminate wrong answers to get to the right answer. At this point we eliminated D & E for the idiomatic issue. What other splits do we have between A, B, & C?

This is where we get into the conditional issue. If we're going to use "if", then we need to also give a consequence to the "if" statement. That's a self-fulfilling rule .

There is no consequence to the "if" statement in A, so we need to use whether for sure. Now we're down to B & C.

"Whether or not" is a suspicious construction because it's usually not necessary to include the "or not." Note that C not only uses this suspicious construction but also has that same issue we mentioned earlier - "it has the capability to broaden" could be much more concisely constructed as "it can broaden." Also, the "can" in front of leave changes the parallelism of the sentence ("can leave" is now parallel to "has the capability," unlike the parallelism in the other answer choices between "broaden" and "leave"), which changes the meaning ever so slightly. 'Nuff said - C is out.

That brings us to B. It correctly uses "whether" instead of "if", it leaves out the "or not" after whether, and it uses the "it can broaden" construction instead of the more verbose "it has the capability to broaden."

Remember: the correct answer has to be completely grammatically correct as well as convey the correct meaning. In our approach, we can't become so focused on solving one issue that we miss the other issues that arise in the answer choices.

I typically avoid this pitfall by always working from wrong to right - I eliminate four wrong answers to get the right one instead of looking for the one that solves the issue that first occurs to me. This approach helps you catch those little grammatical errors that make wrong answer choices wrong.