The rules for GMAT Sentence Correction problems seem fairly straightforward, but a closer examination sheds a good deal of light on why these questions are trickier than they seem. You’re provided with a sentence, at least some of which is underlined. Choice A repeats the underlined portion, and choices B through E are each different ways to phrase that underlined portion. Your job is to select the one choice out of five that is logical in the context of the rest of the sentence and is also free from grammatical error.

And while it may seem basic, the fact that all five choices need to be different ways of phrasing the underlined portion provides some insight into the item writer’s intent: she has to make the five choices different. So, every time a question author writes a new answer choice, she has to change something. And her best strategy to write an interesting and challenging question is to mimic the auto shop with a one-star Yelp rating: they play the “corrupt mechanic. ”

What does a corrupt mechanic do? He fixes things that aren’t broken, and charges you for them. You come in for an oil change and tire rotation, and he suggests that you change your air filter, replace your brake rotors, and flush your catalytic converter…even though none of those things actually has a problem. On the GMAT, Sentence Correction problem writers do the same thing: they “sell you the wrong answer” just like a corrupt mechanic sells you a new muffler. In writing different answers, they take a sentence structure that is valid but not necessarily as common as others, then “fix” that unbroken structure while breaking something else. Consider the two sentences:

Out of France’s passion for cycling evolved the Dauphine Libere, an annual race that each June serves as a prelude to the famed Tour de France.

Vs.

The Dauphine Libere evolved out of France’s passion for bicycling, an annual race that each June serves as a prelude to the famed Tour de France.

In the first sentence, the inverted subject and verb (“evolved the Dauphine Libere” as opposed to “the Dauphine Libere evolved”) is a structure that many GMAT examinees don’t like, but it is in fact a perfectly acceptable way to write that sentence. So what does the corrupt mechanic do? In the second sentence he “fixes” that unbroken structure, but in doing so creates a crucial error: the modifier “an annual race…” now incorrectly modifies “bicycling” and not the Dauphine Libere race. Notice, also, that the unnecessary fix comes at the beginning of the sentence and the new error comes toward the end: by getting people to fixate on that unnecessary repair in the beginning, the Testmaker can convince many examinees to stop reading before they ever get to the crucial error at the end.

In order to beat the corrupt mechanic at this game, you need to go into Sentence Correction problems with a list of necessary repairs in mind. The GMAT frequently tests:

• Modifiers (like the misplaced modifier in the second sentence above)
• Verbs (both verb tenses and subject-verb agreement)
• Pronouns (unclear references and singular/plural errors)
• Parallel Structure (in lists, comparisons, etc.)

Like a savvy car owner, you need to keep these important repairs in mind and look for them first, entertaining suggestions for other fixes (changing idiomatic or sentence structures, for example) only once you’ve checked the major categories off your list. The GMAT Testmaker is masterful at suggesting unnecessary sentence repairs, so your best defense is a proactive mindset of looking for the fixes that you know are common and easy to make. By practicing a few hundred Sentence Correction problems (and perhaps taking a GMAT prep course) you can become an expert in recognizing and fixing the errors listed above; other kinds of differences between answer choices are much more difficult to manage and often have multiple “correct” forms in a given problem. You have to play the Sentence Correction game on your terms!

So don’t let the GMAT’s corrupt mechanic talk you into unnecessary repairs. Study and master the most common error types on the GMAT and look to tackle those “Decision Points” first before you let the exam suggest other differences.