The correct answer is B) provide starting torque. The auxiliary winding on a split-phase, single-phase motor is used to provide additional starting torque. When the motor is first started, the auxiliary winding generates a magnetic field that is out of phase with the main winding, creating a higher starting torque that helps the motor overcome inertia and begin rotating. Once the motor reaches a certain speed, the auxiliary winding is automatically disconnected, and the motor continues running using only the main winding. The other options are incorrect because: A) the auxiliary winding does not keep the motor running if the main winding fails, C) it does not increase the starting current, and D) it does not limit the starting voltage, which is the primary function of the starting capacitor in a split-phase motor.