Answer: C) develop a way to adjust its density so that it can be above and below 1.0 gram per cubic centimeter.
Explanation: Submarine is a kind of special ship that can float above and below water. We know that an object can only float over water when its density is less than the density of water and it would sink if its density is greater than the density of water.
A submarine has tanks in which water is filled if we want to sink it and the water from the tanks is taken out with the help of water pumps to rise the submarine. These water tanks in the submarine helps to adjust its density.
The over all density is increased by filling the water tanks to sink the submarine and the density is decreased by removing the water from the tanks to rise the submarine.
So, option third or C is correct.