If a flagman is waving a yellow lantern up and down, what should the train operator do?

When a flagman is waving a yellow lantern up and down, it indicates that the train operator should proceed with caution to the next flagman. This signal is commonly used to alert the train crew of potential hazards or people working on the tracks ahead. The yellow lantern serves as a warning, so it's imperative for the train operator to reduce speed and maintain a heightened awareness of the surroundings.

In this case, bringing the train under control and blowing a warning would be more appropriate if there were immediate dangers or specific instructions from the flagman, while resuming normal operations in line with fixed signals overlooks the significance of the flagman's warning. Stopping might be excessive unless the situation directly requires it; thus, caution and reduced speed as instructed by the flagman is the best response.