The function of a start winding in a split-phase motor is to a. provide the starting torque. b. reduce the starting current. c. decrease the strength of the magnetic field. d. improve the steady running at full speed.

The most appropriate answer is A, the the start winding on a split-phase motor is to provide a starting torque. A split-phase motor is a single phase electrical motor (common in many household applications such as washing machines and household fans), with two distinct windings on the stator coils, the start windings and the run windings, at 90 degrees apart. When the motor is energised the start coils acts like a second phase (2 phase motor) and helps provide the rotating magnetic field that is necessary to turn the rotor. Once moving, only the run winding (single phase) is required to keep the motor spinning.

The other answers are irrelevant for the starting of the motor.