What factors must be considered for mountain driving brakes?

Answer: B — Total weight, length of grade, steepness of grade, road conditions, and weather

Mountain driving requires careful attention to various factors, including the total weight of the vehicle, the length and steepness of the grade, and the road conditions and weather. Option A is incorrect because only considering the length of the grade would not adequately prepare a driver for safe mountain driving. Option C is incorrect because the weight of the vehicle can also greatly impact the braking system and ability to navigate steep grades. Option D is incorrect because steepness alone does not account for other important factors such as road conditions. Therefore, when driving in mountainous areas, it is essential to consider all of these factors to ensure safe and successful braking.