The GMAT Verbal Reasoning section includes about 13 Sentence Correction questions, which are mixed in with Critical Reasoning and Reading Comprehension.
The directions for Sentence Correction questions look like this:
Directions: Each Sentence Correction question presents a sentence, part or all of which is underlined. Below each sentence, you will find five ways to phrase the underlined portion. The first answer choice repeats the original version, while the other four choices are different. If the original seems best, choose the first answer choice. If not, choose one of the revisions.
In choosing an answer, follow the norms of standard written English: grammar, word choice, and sentence construction. Choose the answer that produces the most effective sentence, aiming to eliminate awkwardness, ambiguity, redundancy, and grammatical error.
Sentence Correction tests your command of standard written English—the rather formal language that is used in textbooks and scholarly periodicals. It’s the language that’s used to convey complex information precisely, as opposed to the casual language that we use for everyday communication. The good news is that you do not need to know every grammar rule for these questions. Errors reflecting certain rules show up repeatedly on the GMAT. Focus on mastering these commonly tested rules—that’s how to get the biggest bang for your study-time buck.