A

Submarines operate based on the principle of buoyancy, which is explained by Archimedes' principle.
Step 1: Understand Archimedes' principle, which states that the upward buoyant force exerted on a body submerged in a fluid is equal to the weight of the fluid that the body displaces.
Step 2: When a submarine wants to dive, it fills its ballast tanks with water, increasing its weight and causing it to displace more water, thus sinking.
Step 3: To surface, the submarine removes water from the ballast tanks, decreasing its weight and allowing it to float again.
Conclusion: Therefore, the construction and operation of submarines fundamentally rely on Archimedes’ principle.