What do Threshold Lights indicate?

Threshold Lights are critical visual cues that indicate the beginning of the operational surface, specifically the runway, for incoming aircraft. These lights are designed to enhance the visibility of the runway threshold, particularly during low-light conditions or adverse weather.

The correct answer reflects that Threshold Lights emit green light, which is universally recognized in aviation as a signal for pilots to know they are arriving at the start of the usable portion of the runway. This is essential for safe landings, as it helps pilots position themselves correctly for landing, ensuring they are on a proper glide path as they approach the runway.

While the other options mention various aspects related to airport operations, such as exit points or taxiway intersections, they do not accurately describe the function and indication provided specifically by Threshold Lights. The distinct function of these lights in marking the runway's beginning is what sets the correct answer apart.