Final answer:
When two students pull on a box with the same magnitude but in opposite directions, the box will not move.
Step-by-step explanation:
When two students pull on a box with the same magnitude but in opposite directions, the box will move in the direction of the net force. The net force is the vector sum of the two individual forces. Since the forces are equal in magnitude but opposite in direction, they will cancel each other out and create a net force of zero. This means that the box will not move, resulting in option A) It doesn't move.