Railway crossings on public roads in Ontario are marked with what?

Answer: C — Red-and-white X signs

Railway crossings on public roads in Ontario are marked with red-and-white X signs, as this has become the standardized symbol for alerting drivers of a railroad crossing. While green circles are often used for pedestrian crossings and blue squares for healthcare facilities, they are not commonly used for railway crossings. Yellow triangles are typically used for warning signs, but not specifically for railway crossings. Therefore, the most suitable and recognizable option for railroad crossings in Ontario is the red-and-white X sign.