Which of the Following Would Violate the Obligation Not to Treat

Which of the following would violate the obligation not to treat others "merely as a means"?

A) Promising to give someone a ride somewhere but failing to do it because your car broke down on the way to pick him or her up.
B) Promising to pay a large reward to anyone who returns your lost dog-no questions asked.
C) Getting someone to promise that they'll help you move later before agreeing to help them move now.
D) Getting someone to help you move by promising to help them move later, even when you know you won't.