Which of the following statements is true of a residual check​ valve?
A. A residual check valve warns the driver of a loss of pressure in one of the two separate systems by lighting the dashboard red brake warning indicator lamp.
B. A residual check valve regulates pressure to the rear brakes in proportion to the pressure applied to the front brakes.
C. A residual check valve lights the red brake warning lamp on the dash if low brake fluid level is detected.
D. A residual check valve helps keep the wheel cylinder sealing cups tight against the inside wall of the wheel cylinder.