The correct answer is: C. rotor and the stator poles of the same polarity.
The coupling angle or load angle of a synchronous motor is the angle between the rotor and the stator poles of the same polarity. This angle is important because it determines the torque produced by the motor. The greater the coupling angle, the greater the torque.
Option A is incorrect because the angle between the rotor and stator teeth is not related to the torque produced by the motor.
Option B is incorrect because the angle between the rotor and the stator poles of opposite polarity is not related to the torque produced by the motor.
Option D is incorrect because the coupling angle is defined as the angle between the rotor and the stator poles of the same polarity.