To protect his train, Guard must first proceed ________ meters in rear and place one detonator in BG in absolute block system. A. 600 B. 800 C. 1200 D. None of these

The correct answer is: A. 600 meters.

In absolute block system, the guard must first proceed 600 meters in rear and place one detonator in BG to protect his train. This is done to ensure that there is no other train on the same track before the train can proceed.

Option B is incorrect because it is the distance that the guard must proceed in rear to place two detonators in BG. Option C is incorrect because it is the distance that the guard must proceed in rear to place three detonators in BG. Option D is incorrect because it is not a valid option.