B. Persian wheels

Explanation:
The Harappan civilization, also known as the Indus Valley Civilization, was one of the most advanced and sophisticated ancient civilizations in the world. They had an efficient system of urban planning, including well-organized cities with advanced drainage systems and a well-developed agricultural system.

The Harappans practiced various methods of irrigation to support their agricultural activities and ensure food production. These methods included the use of canals, wells, and reservoirs. However, they did not employ Persian wheels for irrigation.

Canals:
- Canals were an important method of irrigation employed by the Harappans.
- They constructed a complex network of canals to divert water from rivers and distribute it to agricultural fields.
- Canals played a crucial role in providing a steady supply of water to crops and ensuring their growth.

Wells:
- Wells were another method of irrigation utilized by the Harappans.
- They dug wells to access groundwater and used it for irrigation purposes.
- Wells allowed the Harappans to tap into the water table and irrigate their fields in areas where rivers or canals were not readily available.

Reservoirs:
- Reservoirs were also an integral part of the Harappan irrigation system.
- They constructed large reservoirs to store water during the rainy season and utilize it during dry periods.
- Reservoirs ensured a continuous water supply for irrigation, even during times of water scarcity.

Persian wheels:
- Persian wheels, also known as norias, are a type of water lifting device that consist of a series of buckets attached to a wheel.
- They were commonly used for irrigation in ancient Persia and other regions.
- However, there is no evidence to suggest that the Harappans employed Persian wheels for irrigation.

In conclusion, the Harappans employed canals, wells, and reservoirs as methods of irrigation, but they did not utilize Persian wheels. The Harappan civilization's sophisticated agricultural system relied on these irrigation methods to support their agricultural activities and ensure a stable food supply.