Answer: In this case, both pronouns can be used to complete the sentence as both terms grammatically make sense, however whom is the prefered pronoun.
Explanation:
The difference between “who” and “whom” is the same as the difference between “I” and “me;” “he” and “him;” “she” and “her;” etc. Who, like other pronouns such as I he, and she, is a subject. So, it is the person performing the action of the verb. On the other hand, whom, acts like me, him, and her in a sentence. It is the object. Therefore, it is the person to/about/for whom the action is being done.
But what does that mean? “Who,” the subjective pronoun, is the doer of an action. For example, “That’s the girl who scored the goal.” It is the subject of “scored” because the girl was doing the scoring. Then, “whom,” as the objective pronoun, receives the action. For instance, “Whom do you like best?” It is the object of “like”.
Who should be used to refer to the subject of a sentence.
Whom should be used to refer to the object of a verb or preposition.
