Answer: Option (A) is the correct answer.
Step-by-step explanation:
Surface current is defined as the water at the surface of an ocean moves from one place to another due to the movement of waves.
As warm water is less dense because it degree of compactness is less, therefore, warm ocean currents are usually surface currents. Whereas cold water being more denser remains at the bottom or below the warm ocean currents.
Thus, we can conclude that the statement warm water is less dense than cold water BEST describes why warm ocean currents are usually surface currents.