Answer: (C), Stepping
Answer analysis:
All kinds of CNC milling machines do not use stepper motor as spindle drive motor.
All kinds of CNC milling machines usually do not use DC motors as spindle drive motors.
All types of CNC milling machines usually do not use stepper motors as spindle drive motors. Instead, they usually use AC variable frequency motors or brushless DC motors as spindle drive motors. These types of motors provide more efficient torque and speed control with higher reliability and longevity.
In addition, with the continuous advancement of technology, some new CNC milling machines have also begun to use more advanced linear motors or voice coil motors as spindle drive motors.