Answer: C. A period of drought
Explanation:
A drought is a natural hazard which occurs when a region receives below average precipitation, the region experiences a shortage of water due to the sources of water like lakes, ponds and river get dry. The region is affected by hot and dry climatic conditions, soil becomes compact and looses it's fertility.
C. A period of drought will cause the agrarian society to begin developing the irrigation techniques required to conserve water. As, the agriculture is necessary practice to meet the food requirement of large human population the drought conditions may pose difficulty in irrigating the agricultural field.