The correct answer is: A. Colour light distance.
A P marker is a type of railway signal that is used to indicate the distance to the next colour light signal. It is a white post with a red band at the top, and it is located on the right-hand side of the track. The P marker is usually located 1,000 feet (305 metres) from the next colour light signal, but this distance may vary depending on the specific railway line.
A semaphore distant signal is a type of railway signal that is used to indicate the distance to the next semaphore signal. It is a red and white post with a semaphore arm that can be in either the up or down position. The semaphore distant signal is usually located 1,500 feet (457 metres) from the next semaphore signal.
A semaphore warner signal is a type of railway signal that is used to warn train drivers of a potential hazard ahead. It is a red and white post with a semaphore arm that can be in either the up or down position. The semaphore warner signal is usually located 500 feet (152 metres) from the potential hazard.
The answer to the question is A. Colour light distance.