Answer: d. migration away from productive growing areas
Explanation:
The rice, corn and wheat are the basic food crops. These crops are used for making several dishes their flour as well as the grains of rice and corn are eaten when cooked. These three crops are necessary to be grown on large scale to meet the basic food requirements of the large growing population worldwide. The plant roughage of these three crops can be used to make biofuels. These are used as a fodder crops to feed poultry and cattles for meat harvest.
The demand will also increase when one is migrated to an unproductive region. However, the increased demand is due to decreased supply and not because of increased consumption hence, it will not directly contribute to increase in demand of crops.