The correct answer is: A highly resistive circuit.
At the instant of starting when a D.C. motor is put on supply, it behaves like a highly resistive circuit because the current through the motor is limited by the resistance of the windings. The inductance of the motor also causes a back EMF, which opposes the current flow. This back EMF is proportional to the speed of the motor, so at the instant of starting, when the motor is not moving, the back EMF is zero and the current is limited by the resistance of the windings.
Option B is incorrect because a low resistance circuit would allow a large current to flow, which would cause the motor to overheat. Option C is incorrect because a capacitive circuit would block the flow of current, which would prevent the motor from starting. Option D is incorrect because the motor does behave like a circuit, albeit a highly resistive one.