The correct statement that explains why the total momentum of the soccer balls before and after the collision may not be the same is:
The system has external forces, such as friction and air resistance, acting on it.
This is because external forces can affect the motion of the soccer balls, potentially altering their total momentum during the course of the experiment. In an ideal scenario with no external forces, the total momentum would remain constant, but in a real-world situation, forces such as friction and air resistance can play a significant role.