Which, that and who are relative pronouns. A relative pronoun must refer to the word immediately preceding it. If the meaning of the sentence is unclear, the pronoun is in the wrong position.

Which introduces non-essential clauses; that introduces essential clauses
Who refers to individuals; that refers to a group of persons, class, type, species, or one or more things.

Incorrect: John was met at the door by a strange man, which he, being afraid, opened slowly.

Did John open the man? Probably not. This sentence is definitely confusing, but its meaning can be clarified by adjusting the placement of the nouns in the sentence.

Correct: John was met by a strange man at the door, which he opened slowly out of fear.

It's now clear what John is opening, and why.

On the GMAT, the pronouns "one" and "you," which are part of a class of pronouns called "impersonal pronouns," are often improperly matched with their respective possessive pronouns. You may have heard that using "you" is less proper than using "one," but on the GMAT, all that matters is that the pronouns agree – there's no word-choice preference one way or the other. Look at these examples:

Incorrect: One should have their teeth checked every six months.

Correct: One should have one's teeth checked every six months.

Correct: One should have his or her teeth checked every six months.

Correct: You should have your teeth checked every six months.

Incorrect: One should take your responsibilities seriously.

Correct: One should take one's responsibilities seriously.

Correct: One should take his or her responsibilities seriously.

Correct: You should take your responsibilities seriously.

As long as one isn't paired with your, or you with one's, the sentence is probably correct.

	A summary of how to recognize pronoun errors. Look for: Subject or object pronouns Who or whom Pronoun agreement Relative pronouns

F. Objects of to be verbs

H. Sample Questions