How does an Anti-lock Braking System (ABS) prevent a vehicle from skidding during emergency braking?

1. By applying maximum continuous braking pressure to all wheels simultaneously.
2. By monitoring wheel speed sensors and rapidly modulating (pulsing) the hydraulic brake pressure to prevent the wheels from locking up.
3. By locking the wheels completely to shorten the braking distance.
4. By automatically shifting the transmission into neutral to remove engine drag.