The right answer is:
D) "So, vote for me if you want to see a cleaner campus, better community representation, and a more fun learning environment in our school!"
Alternative D shows the best way to end a campaign president's campaign speech because in it the candidate makes realistic campaign promises that he / she can meet after being elected.
The candidate for class president can not promise that the school will be the best in town and that the school team will win every game because those promises are unrealistic since the candidate has no responsibility in that.