The correct answer is A. T-511.
T-511 is a train order that authorizes a train to start from a non-signaled line. It is used when there is no signal at the beginning of the line or when the signal is not working. T-511 must be issued by a train dispatcher and must be carried by the train crew.
B. T-512 is a train order that authorizes a train to proceed past a stop signal. It is used when the train is unable to stop at the stop signal due to a mechanical problem or other emergency. T-512 must be issued by a train dispatcher and must be carried by the train crew.
C. T/D 602 is a train order that authorizes a train to proceed past a derailment. It is used when the train is unable to stop at the derailment due to a mechanical problem or other emergency. T/D 602 must be issued by a train dispatcher and must be carried by the train crew.
D. A simple memo is not a train order. It is a document that is used to communicate information between employees. A simple memo would not be used to authorize a train to start from a non-signaled line.