The correct answer is: C. Automatic Stop signal
An automatic block system (ABS) is a railway signalling system that prevents trains from colliding by ensuring that only one train is in a section of track at a time. ABS systems typically use track circuits to detect the presence of trains, and signals to indicate whether a section of track is occupied or not.
In ABS SL, the automatic stop signal is the most restrictive signal. It indicates that the train must stop before proceeding. If the automatic stop signal is dispensed with, it means that the train is allowed to proceed without stopping. This can be done in certain situations, such as when the track ahead is clear or when the train is being operated by a qualified driver.
The home signal is the first signal that a train encounters when approaching a station. It indicates whether the train is allowed to proceed into the station. The starter signal is the second signal that a train encounters when approaching a station. It indicates whether the train is allowed to depart from the station.
Therefore, the automatic stop signal is the only signal that can be dispensed with in ABS SL.