Answer:
Gravity
Explanation:
When the ball is falling to the ground, it is already detached from the table, so the table does not exert any force on it.
Gravity is always present, therefore it is acting on the ball (acting downward), so it must be included into the free-body diagram. Apart from that, there are no other forces acting on the ball (if we neglect air resistance, which is negligible, and it is not mentioned in the options given), therefore the only force which has to be included in the diagram is gravity.
