If your brakes fail, you should do which of the following?

Answer: C — Shift into a lower gear

If your brakes fail while driving, shifting into a lower gear can help slow down your vehicle due to engine braking. This is a safer alternative than using the emergency brake, as the emergency brake is not designed to bring a vehicle to a stop in motion. Shifting into a lower gear allows the engine to slow down the vehicle by working against the engine's momentum. This action can buy you some time to maneuver safely off the road or to a stop.