What type of lights signify the threshold and ends of the runway?

The correct answer is that green and red lights signify the threshold and ends of the runway. Specifically, green lights are located at the beginning or threshold of a runway, indicating where the runway starts for aircraft during landing and takeoff. Red lights are situated at the end of the runway, serving as a warning that an aircraft is approaching the end of the landing area. Together, these colors provide crucial visual guidance to pilots during critical phases of flight operations, ensuring safety and proper navigation.

The other options do not represent the correct lighting scheme for runway thresholds and ends. White lights are typically used for runway centerlines and edge lighting, while amber lights are commonly associated with cautionary areas, such as taxiways or in certain zones around airports. Blue lights are primarily used for taxiways to help pilots identify safe routes while on the ground. Understanding this lighting system is essential for pilots and ground crew operating in and around airport environments like O'Hare.