Which sentence correctly uses an objective case pronoun?

AThe person wearing the mascot costume is him.
BThem played basketball for over three hours.
CMalcolm and her went jogging this morning.
DDad was waving at my sister and me.

Verified Answer :

AThe person wearing the mascot costum is him.

C is the best answer.

A, him does not tell us anything
B, the grammar of 'them' is not right
D, 'sister and me' is grammatically incorrect.