The correct answer is: A. Series motor
A series motor should not be started on no-load because it will draw a very high current and overheat. This is because the current in a series motor is directly proportional to the voltage applied to it. When the motor is started on no-load, there is no load on the motor to resist the rotation of the motor. This means that the current in the motor will be very high, and the motor will overheat.
A shunt motor, cumulatively compounded motor, and differentially compounded motor can all be started on no-load without overheating. This is because the current in these motors is not directly proportional to the voltage applied to them. In a shunt motor, the current is determined by the resistance of the shunt field winding. In a cumulatively compounded motor, the current is determined by the resistance of the shunt field winding and the series field winding. In a differentially compounded motor, the current is determined by the resistance of the shunt field winding and the series field winding, but the series field winding is connected in reverse polarity.
In all of these cases, the current in the motor is not high enough to cause overheating when the motor is started on no-load.