Final answer:
The correct minimum distance for separation between aircraft and obstructions on a radar display when 40 miles or more from the antenna is 5 miles, according to FAA regulations.
Step-by-step explanation:
The student's question involves the separation of aircraft from obstructions when they are 40 miles or more from the antenna. According to Federal Aviation Administration (FAA) regulations for aircraft separation, each airplane must maintain a specific minimum distance from another to ensure safety. In airspace where radar is used to monitor and direct aircraft traffic, different separation standards are applied for aircraft that are different distances from the controlling antenna. The correct distance for separation between aircraft and obstructions depicted on the radar display when 40 miles or more from the antenna is 5 miles.