Final answer:
In an anti-lock brake system (ABS), sensors monitor wheel speed and the hydraulic control unit ensures balanced brake pressure. A manual transmission, however, is not involved in the ABS as its main function is to shift gears controlling the vehicle's power and speed.
Step-by-step explanation:
Referring to the primary components of the anti-lock braking system, namely the sensors for monitoring wheel speed, the hydraulic control unit, and some feature to avoid locking of brakes, the one element not involved is a manual transmission system (Option D). It's important to understand that an anti-lock brake system (ABS) is essentially intended to prevent the wheels from locking while braking and thereby to maintain tractive contact with the road surface. Anti-lock brakes work through a system of sensors that monitor wheel speed. If these sensors detect that one wheel is slowing down more quickly than the others, indicating it's about to lock up, the system reduces brake pressure to that wheel. It does this using the hydraulic control unit. Therefore, sensor and hydraulic unit are integral parts of the ABS. But a manual transmission system does not factor into the operation of an ABS. Its task is rather to enable the driver to shift gears and thus control the power and speed of the vehicle.
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