Concept:Irrigation is the artificial supply of water to farmlands.
It becomes necessary when rainfall is low, unreliable, or when food demand is high.
Explanation:Irrigation practice is determined by physical and economic factors.
Unreliable rainfall encourages irrigation because farmers cannot depend fully on rain for crop growth.
The need for more food also promotes irrigation since it helps to increase crop yields on available land.
The presence of fertile soil supports irrigation because the land can return good harvests when water is supplied.
High rainfall, however, does not encourage irrigation.
Where rainfall is abundant and reliable, crops naturally receive enough water, so irrigation is not required.
Thus, high rainfall is the factor that is not an influence on the practice of irrigation.
Answer:B. high rainfall