Correct Option (D)
The passage explicitly states that "Historically, the biggest challenge to world agriculture has been to achieve a balance between demand for and supply of food." This fundamental issue is then elaborated upon throughout the text, discussing its implications for individual countries and the global community, particularly in relation to hunger and purchasing power. Thus, the core challenge identified is the equilibrium between food demand and supply.
Incorrect Options:
The passage does not identify finding sufficient land for agriculture or expanding food processing industries as the primary challenge to world agriculture. These aspects are not emphasized as the overarching concern in the provided text.
While eradicating hunger in underdeveloped countries is a critical global issue and a direct consequence of the demand-supply imbalance, the passage frames the biggest challenge as the underlying difficulty in balancing food demand and supply. Hunger is presented as an outcome of this imbalance, especially when compounded by a lack of purchasing power, rather than the fundamental challenge itself.
The passage does not discuss the challenge of achieving a balance between the production of food and non-food items. This topic is not addressed within the context of the biggest challenge to world agriculture as presented in the text.