A rigid sphere is kept stationary on the seabed. Once the sphere is let go, it moves up to the surface of the sea. The seawater has a constant density. Which statement about the sphere, from the moment it is released until it reaches the surface, is correct?
- AThe sphere always moves with constant acceleration.
- BThe sphere always moves with constant velocity.
- CThe upthrust on the sphere always decreases.
- DThe upthrust on the sphere is always constant.