What must you do when red lights are flashing at a railway level crossing?

Answer: B — Stop until the lights stop flashing

When red lights are flashing at a railway level crossing, it is essential to stop until the lights stop flashing. This is a critical safety measure designed to protect both drivers and pedestrians from the dangers of an oncoming train. The flashing red lights serve as a clear signal that a train is approaching or is already in the crossing area. Ignoring this signal and proceeding could lead to a potentially fatal collision, as trains can travel unexpectedly fast and do not have the ability to stop quickly. Therefore, to ensure the safety of everyone and to comply with traffic regulations, stopping until the flashing lights cease is the appropriate action to take.