A ball is dropped from the edge of a cliff. Which of the following statements is correct?

(There may be more than one correct answer!)

(A) Gravity does work on the ball as it falls.

(B) The gravitational potential energy of the ball decreases as the ball falls.

(C) The gravitational potential energy of the Earth decreases as the ball falls.

(D) The gravitational potential energy of the system of ball

+ Earth decreases as the ball falls

The correct option are (A) and (D).
When the ball is dropped from the edge of a cliff, the force due to the Earth’s gravity will always act in the downward direction. Therefore, gravity does work on the ball as it falls. Thus option (A) is correct.
Gravitational potential energy is the energy acquired by a body by virtue of its position in the gravitational field. Since the ball is falling from the edge of a cliff, the position of the ball will respect to the center of the Earth decreases. This will make to decrease the gravitational potential energy of the ball and Earth system. Thus, when a ball is dropped from the edge of a cliff, the gravitational potential energy of the system of ball + Earth decreases as the ball falls. Thus option (D) is correct.
From the above observation, both option (A) and (D) are correct.