The correct answer is: A. 25 kmph.
The automatic block system (ABS) is a railway signaling system that prevents trains from colliding by ensuring that there is always a safe distance between them. In ABS, each section of track is divided into blocks, and a train can only enter a block if the block ahead is clear. The ABS system uses a variety of methods to detect trains, including track circuits, axle counters, and radio signals.
The T/B 912 is a type of ABS system that is used in India. In T/B 912, the speed of a train is limited to 25 kmph when the view ahead is clear with a straight line. This is to ensure that the train can stop safely in the event of an obstacle.
The other options are incorrect because they are not the speed limit for a train in T/B 912 when the view ahead is clear with a straight line.