The correct answer is A. In a parallel axis single reduction gear, the drive pinion is the smaller of the two gears and rotates at a relatively high-speed, while the driven gear is the larger of the two gears and rotates at a relatively low-speed. This configuration allows the gear system to reduce the rotational speed from the drive shaft to the output shaft, providing the necessary torque multiplication for the application. The other options are incorrect because they describe the opposite arrangement, where the larger gear is the drive pinion and the smaller gear is the driven gear, which is not the typical configuration for a parallel axis single reduction gear.