In case of synchronous motor, which of the following are true?a. Synchronous motor is not self-startingb. If the rotor poles are excited by field current and the stator terminals are connected to AC supply, motor vibrates.c. Variable frequency supply is used to start synchronous motor.d. By using frequency converter, a synchronous motor can be brought from standstill to its desired speed.

• A. Only a and b are true
• B. Only b and c are true
• C. All are true
• D. None of the above