Which sentence contains a pronoun that is not in the proper case?
a) mom yelled upstairs and asked all three of her children to come down and clean up their sticky messes.
b) the clevelands' dogs, martha and max, usually behave, but sometimes they also like to get into mischief.
c) the little girl begged and pleaded to be allowed to wear her new pink dress and hat to the boy's party.
d) the sudden protests against the mayor that erupted in the city caused friction between he and his closest advisors.