Question

Choose the option that best fills in the blank:
_______ is knocking on the door?

• A. Whom
• B. Who
• C. Which
• D. Why

Answer 1

Answer: (B)

Who

The given statement is interrogative, hence an interrogative pronoun is required. Interrogative pronouns help to ask questions and at the same time do the work of the nouns that they stand for. From the options, 'who' when placed, helps to ask about the person knocking the door. 'Who' is used for a person in the subject form, the subject performs an action toward an object, and who performs the action "knocking", hence option B is correct. 'Whom' is a pronoun in the objective case, it is at the receiving end of the action, like in 'You were speaking to whom?', hence it isn't required here and option A is incorrect. 'Which' usually refers to non-living beings and rarely refers to a person, when referring to a specific person it is followed by that noun, like, 'which woman was it?' Here it does not help in asking about the person, hence option C is incorrect. 'Why' is not an interrogative pronoun, it does not refer to a person or a thing, it's a question word that asks 'for what reason'. The statement does not focus on reason, but a person, hence option D is incorrect.