Question

A ball rolls down from the top of a grassy hill, reaches the bottom of the hill, continues to roll, and then starts to slow down and comes to a stop. What forces caused this ball's motion?

Answer 1

the answer is gravity

Answer 2

Gravity caused the ball to roll down from the top of the hill.

Friction with the ground, the grass, and the air, and the energy required
to push grass out of the way, caused it to slow down and come to a stop.