When the brake pedal is suddenly released, a residual check valve provides enough pressure to hold the wheel cylinder cups ______

The correct answer indicates that a residual check valve plays a critical role in maintaining enough pressure to hold the wheel cylinder cups tightly against the cylinder after the brake pedal is suddenly released. This functionality ensures that the brake system remains responsive and capable of quickly re-engaging when the driver presses the brake pedal again.

By keeping the cups pressed tightly against the cylinder, the system minimizes the chances of air entering the brake lines, which could lead to a loss of brake effectiveness. This pressure retention also allows for a quicker response time when braking is required again, thereby enhancing overall safety and performance of the braking system.

The other choices do not accurately represent the function of the residual check valve in the braking system, as none describe this scenario of maintaining contact and stability necessary for optimal brake operation.