The correct answer is B) provide reduced voltage for starting. Autotransformers used with autotransformer starters on large AC motors function to provide a reduced voltage during motor starting. This reduced voltage helps limit the high inrush current that would occur if the motor were started directly on full line voltage. The lower starting voltage reduces the starting torque but allows the motor to be gradually brought up to full speed and voltage, protecting the motor and electrical system from excessive currents. The other options are incorrect because: A) increased torque is not the purpose of the autotransformer, C) speed control is not the function, and D) increased voltage would not be desirable for starting a large motor.