The correct answer is: A. Not-self starting
Synchronous motors are not self-starting because the rotor must be turned to the synchronous speed by an external source before it can start to generate its own torque. Once the rotor is up to speed, it will continue to rotate at the synchronous speed as long as the applied voltage is maintained.
Option B is incorrect because synchronous motors can be started by using an external source of power to turn the rotor to the synchronous speed.
Option C is incorrect because synchronous motors are not essentially self-starting. They require an external source of power to start.
Option D is incorrect because synchronous motors are not self-starting.