A submarine or a ship can float because the weight of water that it displaces is equal to the weight of the ship. ... To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air (see animation below).
Answers:
It would seem that it would be B..... you'd have to decrease the buoyant force by removing the air from the dive tanks and filling them with water. And in a way it's C - by allowing water into the dive tanks, you are balancing the weight of the sub with the water around it.
