Fill-In-The-Blank: Based on the text, it was more difficult for workers to work in the Andes Mountains because the air was
A. too hot
B. thinner
C. full of moisture

The Andes are some of the tallest, starkest mountains in the world. Yet the Incas, and the civilizations before them, coaxed harvests from the Andes’ sharp slopes and intermittent waterways. They developed resilient breeds of crops such as potatoes, quinoa and corn. They built cisterns and irrigation canals that snaked and angled down and around the mountains. And they cut terraces into the hillsides, progressively steeper, from the valleys up the slopes. At the Incan civilization’s height in the 1400s, the system of terraces covered about a million hectares throughout Peru and fed the vast empire.