Which statement is a good example of assertiveness?

A) “I’m not sure if I will have time to do your homework and mine before I go to bed.”
B)“Okay, I’ll do your homework, but this is the last time."
C) “We each have an assignment to complete. You need to take care of yours so you actually learn something.”
D) “You are out of your mind if you think I am going to do your homework for you!”