A Sentence Correction question looks like this:

1. When Charlene goes to the park, she likes to run, swim, and to play basketball.

A. she likes to run, swim, and to play basketball
B. she likes to run, swim, and play basketball
C. she likes running, to swim, and to play basketball
D. she likes running, swimming, and to play basketball
E. she likes all of the following, to run, swim, and to play basketball

You are given a sentence with one section underlined, and five answer choices. The underlined portion is reproduced five different ways in the answer choices - choice A will always be identical to the underlined portion of the sentence. Your task is to find the answer choice which is most grammatically correct according to the rules of Standard Written English. Sometimes more than one answer choice will appear to be free of grammatical errors. This is not a mistake. Style conventions must be taken into consideration as well. When this occurs, you must look for the answer that is clearly expressed and concise.

800score Three-Step Method to Sentence Correction questions:

1. 
   Read the entire sentence. Do not simply read the underlined part of the sentence, because context may be important in determining the correct answer. As mentioned above, choice A will always be a copy of the original underlined part of the sentence. If you cannot find any errors, grammatical or otherwise, in the original sentence, choose A, and move on. Don't worry about spelling, capitalization, or punctuation; they are not covered in Sentence Correction questions. If you do find an error in the underlined portion, or if you're not 100% sure, proceed to step two.
   
   
2. 
   The GMAT tests only a limited number of grammar error types. After you've read the sentence, look for clues indicating which grammar rule the question is testing. These grammar rules, and the clues to look for, will be covered in more detail in the next section. Keep an eye out for:
   Agreement Issues: Look for pronouns, verbs, and nouns: do they agree?
   Modifiers: Look for introductory phrases set off by a comma: is the modifier used correctly?
   Parallels: Look for commas separating words in a list, as well as expressions such as not only...but also, both...and, either...or, neither...nor: is everything parallel?
   
   
3. 
   After you've dissected the question, compare answer choices and note the differences. Look for the answer choice that preserves the meaning of the original sentence, and fixes its errors without creating new errors. Eliminate answer choices with grammar errors.

Now that you have a method for approaching the questions, it's time to move on to specifics: how to recognize and correct the seven common grammar errors found in the GMAT.

Glossary

Seven Types of Errors in the Sentence Correction Section