Any structure that is ______ feet or more must be marked (lighted).

The requirement for marking or lighting structures that are a specific height is focused on safety and visibility for air traffic. A structure that is 200 feet or more above the ground is designated as a height requiring such markings in order to prevent accidents involving aircraft, particularly in the vicinity of airports and flight paths. This guideline comes from regulations set by the Federal Aviation Administration (FAA), which mandates that any obstruction to navigable airspace should be clearly identified.

Structures below this height typically do not pose as significant a risk to air traffic, which is why the threshold is set at 200 feet. Marking and lighting these taller structures helps ensure they are visible to pilots during both day and night, significantly reducing the risk of collisions. Therefore, the choice reflecting 200 feet aligns with safety regulations and best practices in aviation and construction.