Answer:
They were in a hurry and did not have time to pack properly.
A. "Whom" is an object pronoun is actually the only one that is correct. This is because for B. whom could be an object of a preposition if it was in a sentence with "to whom". For C., who is only a subject pronoun. If it were an object pronoun, a sentence would be like this: "To who does the present go to?".
