The correct answer is: B. Siding Line
A siding line is a short railway track that branches off from the main line. It is used for trains to stop and wait, or to be moved to another part of the railway network. Siding lines are often used to load and unload goods, or to repair trains.
A loop line is a railway track that runs parallel to the main line. It is used to allow trains to pass each other, or to allow trains to wait while another train passes. Loop lines are often used on single-track railways.
The main line is the main railway track. It is used for trains to travel between different stations. The main line is usually the busiest railway track, and it is important to keep it clear for trains to travel through.
It is not safe to admit a train with hot axle on the main line because it could cause a fire or derailment. The hot axle could also damage the track. A siding line is a safer place to admit a train with hot axle because it is not as busy and there is less risk of causing an accident.