The correct answer is: A. whose
The sentence is about my uncle, and the question is about his car. The answer must be a pronoun that refers to my uncle, and it must also be a pronoun that can be used to refer to possession. The only pronoun that fits both of these criteria is “whose.”
The pronoun “which” can be used to refer to things, but not to people. The pronoun “whom” is used to refer to people who are the objects of actions, but in this sentence, my uncle is the subject of the action, not the object. The pronoun “who” can be used to refer to people, but it cannot be used to refer to possession.
Therefore, the correct answer is “whose.”