Name the underground water channels developed during ancient times in which water drains using gravity via a slope for the purpose of irrigation.

Correct option is B

Correct Answer: (B) Qanats

Explanation:

• Qanats are underground water channels that were developed in ancient times, primarily in Persia (modern-day Iran) and other arid regions.
• These channels were designed to transport water from an aquifer or water well, using gravity via a slope to irrigate land.
• The qanat system was especially useful in desert areas, where surface water was scarce, allowing civilizations to harness underground water resources.

Other Options:

•  Tributaries: These are smaller rivers or streams that flow into a larger river, not underground water channels.
•  Tunnels: Tunnels are passageways dug into the earth but are not specifically used for water drainage or irrigation.
•  Rivers: Rivers are surface water bodies and not underground channels.