The correct response is:
The stationary soccer ball will begin moving downfield and the ball that struck it will slow down.
When the moving soccer ball (with a force of 1.2 kN) collides with the stationary soccer ball, the force exerted by the moving ball will transfer momentum to the stationary ball, causing it to move downfield. Meanwhile, the ball that was initially moving will lose some of its momentum and thus slow down after the collision.