The correct answer is: c. Areas at low latitudes have the warmest water because they receive the most direct sunlight.
The warmest surface waters can be found in and around the Equator. The reason for that is that this parts of the world receive the most direct sunlight, with the sunlight falling at an angle of 90° or close to it. Because the sunlight is more concentrated, these areas are much warmer than the rest of the planet, having high temperatures throughout all of the year, where there isn't change of seasons, or its only dry and wet season (but the wet one is also warm). As everything else, the water too is warmer in these ares because of the more direct sunlight, and these are the ares where the warm ocean currents actually start.