What should a driver do if their brakes fail while driving?

Answer: B — Gradually downshift and use the parking brake if necessary

When a driver experiences brake failure, the most effective response is to gradually downshift to reduce speed and use the parking brake if necessary. This method allows the driver to maintain control of the vehicle while slowing it down safely. Gradual downshifting reduces speed without causing a sudden loss of control, and the parking brake can provide additional braking force, though it should be applied carefully to avoid skidding. Steering off the road may not always be a viable option, especially if there are obstacles or other vehicles nearby. Calling for roadside assistance is a good long-term solution but does not address the immediate need to control the vehicle. Braking suddenly can lead to loss of control, especially in the absence of functional brakes, making it a risky choice. Thus, the combination of gradual downshifting and utilizing the parking brake is the most proactive and safe strategy in the event of brake failure.