The correct answer is B) constant potential, variable current DC sources. In a shunt wound, series wound, or compound wound DC motor, the voltage potential (or voltage input) is kept constant, while the current input is allowed to vary based on the load and operating conditions of the motor. This allows the motor to draw the necessary amount of current to meet the torque and speed requirements, while maintaining a steady voltage supply. The other options are incorrect because variable potential (A) or constant current (C and D) sources are not the standard design for these types of DC motors. The constant potential, variable current configuration is the most efficient and effective way to power these DC motor types.