The correct answer is: A. to
The word “aims” is a verb that means “to direct one’s efforts toward a particular goal.” In this sentence, William is saying that he is directing his efforts toward winning at least a consolation prize. The preposition “to” is used to indicate the goal or purpose of an action. In this case, the goal is to win at least a consolation prize.
The other options are incorrect because they do not make sense in the context of the sentence. The preposition “at” is used to indicate a location or position. The preposition “on” is used to indicate a surface or area. The preposition “for” is used to indicate a purpose or reason.
In conclusion, the correct answer is: A. to