The correct answer is: None of these
During emergency, in the absence of tail board, no flag can be used with the DRM.
The DRM (Directional Reflector Marker) is a device that is used to mark the location of a hazard on the railway. It is typically a white or yellow disc with a reflective surface. The DRM is mounted on a post or pole and is visible from a distance.
The tail board is a piece of equipment that is attached to the back of a train. It is used to warn other trains that the train is stopped. The tail board is typically a red flag or light.
In the event of an emergency, the DRM can be used to mark the location of the hazard. However, if the tail board is not available, no flag should be used. This is because a flag could be mistaken for a signal and could lead to a collision.
Instead, the DRM should be used in conjunction with other safety measures, such as flares or warning lights.