Which interrogative pronoun best completes the sentence? How is the pronoun used? For __________ is your sister waiting? A. whom; object of a preposition B. whose; possessive C. who; subject D. whom; direct object
Out of all the pronouns, "whom" makes the most sense grammatically. This allows us to narrow it down to A or D. In order for it to be the object of a preposition, there would have to be a preposition in front of it. "For," however is not a preposition. In fact, there isn't a preposition in the whole question. This leaves us with option D, which is the correct answer. You can better tell it's a direct object if you flip the sentence around a bit. Your sister is waiting for whom? "Whom" is essentially receiving the action. "Whom" is what your sister is waiting for. Answer: D. whom; direct object.