The correct answer is D) provide starting torque. Synchronous motors rely on the alternating current (AC) supply to create a rotating magnetic field, which interacts with the magnetic field of the rotor to produce torque. However, synchronous motors cannot start on their own from a standstill due to this reliance on the rotating magnetic field. The squirrel cage windings installed on the synchronous motor rotor provide the necessary starting torque to overcome this limitation. These windings act like an induction motor during the start-up phase, generating their own magnetic field and producing the required starting torque to get the motor rotating. Once the motor reaches a certain speed, the squirrel cage windings become less effective, and the synchronous motor then operates on the principle of the rotating magnetic field. The other options are incorrect because the squirrel cage windings do not provide excitation (A), eliminate slippage (B), or increase efficiency (C) in a synchronous motor. Their primary function is to enable the motor to start and reach the synchronous speed.