Which national park in Kentucky preserves the world's longest known cave system, with more than 400 miles of explored passageways?

• A Carlsbad Caverns
• B Jewel Cave
• C Mammoth Cave National Park ✓
• D Wind Cave

Mammoth Cave is more than twice as long as the second-longest cave system (Sac Actun in Mexico) and has been a tourist attraction since 1816.