Crossing railway tracks is prohibited under which of the following circumstances?

Answer: D — All of the above

Crossing railway tracks is strictly prohibited under all of the listed circumstances because each scenario represents a significant safety hazard. When a train is approaching, it poses an immediate risk of a collision due to the speed and the mass of the train, which makes it very difficult to stop in time. The movement of the gates indicates that a train is either present or imminent, and attempting to cross during this time could lead to an accident, as the gates are designed to control traffic and enhance safety by preventing crossings at dangerous times. Additionally, if a flagman is directing traffic to stop, this indicates that there is a safety concern that necessitates halting vehicles to protect them from oncoming trains. Therefore, all of these circumstances collectively highlight why crossing railway tracks is prohibited—they are all measures intended to ensure the safety of drivers and pedestrians.