The correct answer is: A Class/IBS.
TSL stands for Train Service Loop. It is a type of train service that allows trains to travel in both directions on the same track. This is done by using a cross over facility, which is a piece of track that allows trains to switch from one track to another.
A Class/IBS is a type of train that is equipped with a TSL system. This system allows the train to automatically switch tracks when it reaches a cross over facility. This makes it possible for the train to travel in both directions on the same track, without the need for a human operator to switch the tracks manually.
C Class/IBS and D Class/IBC are types of trains that are not equipped with a TSL system. This means that they cannot travel in both directions on the same track. They can only travel in one direction, and they must be switched to the other track manually by a human operator.
Therefore, the correct answer is: A Class/IBS.