The correct answer is C. Centrifugal switch.
A centrifugal switch is a switch that is used to disconnect the starting winding of a single phase motor when the motor reaches a certain speed. This is done to prevent the starting winding from overheating. The centrifugal switch is usually located on the motor shaft and is activated by centrifugal force.
A magnetic relay is a switch that is used to control a circuit by means of a magnetic field. The magnetic relay is usually used to control a high current circuit with a low current circuit.
A thermal relay is a switch that is used to protect a circuit from overheating. The thermal relay is usually used to control a motor by disconnecting the power to the motor if the motor overheats.
None of the above is not the correct answer because it does not specify which device is used to disconnect the starting winding of a single phase motor.