The correct answer is: D. None of these.
During failure of signals and communications in DL automatic area, the authority to proceed is the train driver. The train driver must use their own judgment to determine whether it is safe to proceed. They must consider factors such as the speed of the train, the distance to the next signal, and the visibility conditions.
T/D 912 is a train order that authorizes a train to proceed to a designated point. T/A 912 is a train order that authorizes a train to proceed to a designated point after receiving a radio message from the dispatcher. T/B 912 is a train order that authorizes a train to proceed to a designated point after receiving a visual signal from the dispatcher.
However, none of these train orders are applicable during failure of signals and communications in DL automatic area. In this situation, the train driver must use their own judgment to determine whether it is safe to proceed.