The correct answer is: Caution order.
A Caution order is issued to the Loco Pilot from the station in rear if the Distant signal of a Gate becomes defective in off condition. This is because the Loco Pilot needs to be aware of the potential hazard and take appropriate precautions.
A Reminder order is issued to the Loco Pilot when the Distant signal is not working properly. This is to remind the Loco Pilot to be extra cautious when approaching the signal.
A Nil caution order is issued to the Loco Pilot when the Distant signal is working properly. This means that the Loco Pilot can proceed without any further caution.
None of these is the correct answer because it does not specify the type of order that is issued to the Loco Pilot.