How can vessels further from land detect inland mountains?

• A. By using RADAR to detect mountains over the top of the coastal hills.
• B. By relying on visual observations at high altitude.
• C. By listening for echoes from inland ranges.
• D. By using sonar to measure terrain.

Answer: (A)

Radar lets a vessel detect distant, elevated terrain by sending radio waves that travel in straight lines and reflect off objects. When mountains inland rise above the line of sight blocked by the coastline and coastal hills, they poke above the horizon from the ship’s point of view. The radar beam can still reach them, bounce off their slopes, and return a signal to the set. Because the peaks stand taller than the intervening terrain, they become visible to the radar even though you can’t see them with the naked eye from that distance. Visual observations would be blocked by the coast and hills, sonar is for underwater terrain, and listening for echoes isn’t how land features are detected. So using radar to detect mountains over the top of the coastal hills is the practical method.