What is the function of the hydraulic modulator (valve block) in an Anti-lock Braking System (ABS)?

1. To increase brake pedal stroke.
2. To modulate (apply, hold, and release) hydraulic brake pressure to individual wheels to prevent wheel lockup.
3. To distribute braking force between the front and rear axles based on vehicle load.
4. To bleed trapped air bubbles from the brake lines automatically during normal driving.