Under what conditions should the brakes be able to stop a vehicle on a grade?

The correct answer highlights the importance of brake functionality when a vehicle is parked, particularly on an incline. When parked on a grade, it is essential that the brakes are able to hold the vehicle stationary to prevent it from rolling downhill. This is crucial for safety, as a vehicle that rolls away can pose a serious risk to other road users, pedestrians, and property.

In situations where the vehicle is parked, especially on slopes or grades, adequate braking capability is essential to ensure stability. Vehicles typically have a parking brake designed specifically to keep the vehicle secure in that position. Proper maintenance and testing of this system help ensure that it can effectively prevent movement when the vehicle is stationary.

Focusing on other options, while it’s true that brakes should function effectively when a vehicle is in motion (as noted in choice D), the context of the question emphasizes the requirement for secure parking. Furthermore, the ability to stop a vehicle at any speed (noted in option B) is not a scenario that reflects the specific condition of being parked. Meanwhile, option C limits the application of brakes solely to downhill instances, which overlooks the necessity of proper braking performance when parked on any grade, whether uphill or downhill.