(C) Must act on different objects is the correct answer.
If action and reaction forces act on the same object, both of them would get cancelled and hence, would result in no motion of the object.
So, it is certainly not "may" but "must".
Action and reaction forces may differ in their magnitudes but are always opposite in direction.
Firing a bullet, breaking of a shell into pieces, a walk on floor and hitting a ball against the wall are a few good example to prove this.