What federal requirement must the braking system of a vehicle meet?

Answer: B — Must work evenly

The braking system of a vehicle must work evenly to ensure that it stops safely and effectively under various driving conditions. This means that when the driver applies pressure to the brake pedal, the braking force should be distributed evenly across all wheels to prevent skidding or losing control of the vehicle. An even brake system allows for better handling and stability, especially during emergency stops or when navigating curves. While the other options might seem relevant, they do not reflect the core requirement set by federal guidelines for braking systems. For instance, the notion of stopping within 30 feet can vary based on vehicle type and speed, and while electronic controls can enhance braking, they are not a mandated feature. An automatic fail-safe might be a good characteristic, but it's not a specific federal requirement as mandated for braking systems. Thus, an even working braking system is critical for safety and compliance with driving regulations.