Which of the following is NOT a factor that affects stopping distance?

The choice indicating engine size as not being a factor that affects stopping distance is correct because stopping distance is primarily influenced by aspects related to the vehicle's dynamics and the driver's behavior rather than the engine's specifications. Key factors that impact stopping distance include vehicle weight, which affects momentum; driver reaction time, which is the interval between recognizing a need to stop and initiating the action; and road incline, which impacts how quickly a vehicle can come to a complete stop when traveling downhill or uphill. Engine size does not directly affect the ability to stop a vehicle; instead, it may influence acceleration and vehicle performance but has no bearing on braking effectiveness or distance.