d. Neither Technician A nor B is correct. A passive-type wheel speed sensor is not magnetic. It uses an optical sensor to measure the rotational speed of the axle. The sensor measures the frequency of a toothed sensor ring attached to the axle and not the magnetic field of the sensor ring. So, neither Technician A nor B is correct.
The type of sensor ring can vary depending on the type of application and sensors involved. However, in the case of passive-type sensors, the sensor ring is not magnetic.