The single-most crucial type of Sentence Correction error, Modifiers, Comparisons, and Verb Tenses all share one thing in common: you do not need to be an expert editor to recognize that this sentence is illogical! The introductory phrase in this sentence, “the single-most type…” is clearly meant to describe one item, but the rest of the sentence lists three. This does not make logical sense! Technically you’d call this a modifier error, in that the modifying phrase to begin the sentence – recognizable because it begins the sentence, is separated by a comma, and does not include its own subject and verb (note: these aren’t essential characteristics of any modifier, but they are one surefire way to identify a commonly-occurring type of modifier in which SC errors often crop up) – does not logically modify the noun that follows.
If you want to get really technical, it is an appositive modifier (a noun phrase used to describe another noun), but the GMAT will never require you to describe the grammatical terminology behind it. If you can recognize that “this is wrong – logically it doesn’t make sense”, you can eliminate this answer choice and move on. And even if you do choose to dig deeper into grammatical technicalities, don’t lose sight of your logical focus. Consider this example, often mistaken by students as incorrect:
In order to break the world record in the 100 meter dash at next summer’s Olympics, Tyson Gay will need to run faster than Usain Bolt ran at the 2009 World Championships.
Many a GMAT student has looked at a sentence like this and viewed the comparison as incorrect, citing “parallelism” as their primary concern. “You cannot compare a future tense verb to a past-tense verb…they’re not perfectly parallel!” they’ll claim. But, again, ask yourself about the logic: is there any logical way to put these two actions in the same tense? From where we are standing today, “next summer’s Olympics” must be in the future, and 2009 must be in the past. We simply cannot put them in the same verb tense. For comparisons, the two items must be logically comparable, but they need not be perfectly parallel to the umpteenth grammatical degree. This sentence is wrong:
In order to break the world record next summer, Tyson Gay’s time will need to be faster than Usain Bolt at the 2009 worlds.
Here we are comparing Gay’s time to Bolt, the person, and this is not a logical comparison. Logic is your primary goal on these questions, so look for clearly illogical modifiers, sequences, comparisons, etc. and you will nearly always be able to avoid having to dig that much deeper for grammatical jargon or expertise. If the words “gerund” and “participle” are not currently part of your vocabulary, you probably don’t need them to be when you take the test, either.