The correct answer is: A. Track Circuit.
A track circuit is a device used on railways to detect the presence or absence of a train on a section of track. It is a safety device that prevents trains from colliding.
During thick or foggy weather or night, visibility is reduced. This makes it difficult for train drivers to see if there is a train ahead of them. To prevent collisions, track circuits are used to detect the presence of a train on a section of track. If a train is detected on a section of track, the track circuit will send a signal to the train’s control system, which will prevent the train from moving forward.
Track circuits are also used to provide train detection for automatic train control (ATC) systems. ATC systems use track circuits to monitor the position of trains on the track and to prevent trains from colliding.
Track circuits are an essential safety device on railways. They help to prevent collisions and to ensure the safe operation of trains.
The other options are incorrect because they are not devices that are used to detect the presence of a train on a section of track.