The correct answer is B) provide a wide range of combustion. A variable capacity, pressure atomizing, fuel oil burner functions to provide a wide range of combustion. This allows the burner to adjust the fuel flow and atomization to accommodate different load conditions and maintain efficient combustion over a wide operating range. The other answer choices are not the primary functions of this type of burner. Option A is related to maintaining fuel temperature, option C is about maintaining fuel return pressure, and option D is about achieving smokeless atomization, which are secondary or supporting functions rather than the main purpose of a variable capacity burner.