With which system in a passenger car does the anti-lock "ABS" operate?

The illustration shows a car's instrument panel with the ABS warning light marked with an arrow. The anti-lock braking system ABS works with the braking system - answer B, not with the suspension (A) or the steering system (C).

ABS stands for Anti-lock Braking System, a system that prevents the wheels from locking during braking. Its sensors measure the rotation speed of each wheel, and when one starts to lock, the control unit uses the modulator valves to lower the fluid pressure in that wheel's brake line for a fraction of a second and then restores it at once, even a dozen or more times a second. A rolling wheel keeps its grip and responds to turning the steering wheel, so during emergency braking you can steer around an obstacle; a locked wheel would just slide in a straight line. The ABS warning light comes on for a moment after you switch on the ignition as a test; if it stays on while driving, the system is switched off, but the normal brakes work - you then brake more carefully, without locking the wheels, and drive to a garage. Adaptive systems work with the suspension, and power steering works with the steering system - not ABS.