The diagram shows two opposite horizontal forces of magnitude 2.1 N and 6.4 N acting on a toy cart on a flat, horizontal track.

Which of the following statements could be correct?
I. The cart is accelerating and moving to the right. II. The cart is decelerating and moving to the left. III. The magnitude of the resultant force is 4.3 N.
I and III only
II and III only
I, II and III
III only