None of these choices names anything that keeps the water in the bucket.
A. Gravity always pulls down. When the bucket is at the top of the circle, gravity is trying to pull the water down, OUT of the bucket.
B. Acceleration is not a force. Acceleration is produced by a force.
C. Centripetal force always pulls toward the center of the circle. When the bucket is at the top of the circle, centripetal force is trying to pull the water down, OUT of the bucket.
D. Mass is not a force.
None of these choices names anything that keeps the water in the bucket.
