The correct answer to the question is option 'C', D. Whittlesey.

Explanation:
Agricultural regions are geographical areas with distinct characteristics and conditions that make them suitable for different types of agricultural activities. These regions are determined based on factors such as climate, soil conditions, topography, and water availability. The major agricultural regions of the world were first delineated by D. Whittlesey.

1. Introduction to D. Whittlesey:
D. Whittlesey refers to Derwent Whittlesey, an American geographer who made significant contributions to the field of agricultural geography. He conducted extensive research and analysis to identify and classify the major agricultural regions of the world.

2. Importance of Agricultural Regions:
Understanding agricultural regions is crucial for various reasons:
- It helps in identifying the type of crops or livestock that can be grown or raised in a particular region.
- It aids in understanding patterns of agricultural production and distribution.
- It assists in analyzing the impact of environmental factors on agricultural practices.
- It provides insight into the relationship between agriculture and economic development.

3. Delineation of Agricultural Regions:
D. Whittlesey used a comprehensive approach to delineate the major agricultural regions of the world. He considered several factors, including climate, soil fertility, topography, and water availability.

4. Whittlesey's Classification:
Whittlesey classified the major agricultural regions into eleven categories:
1. Intensive subsistence agriculture
2. Plantation agriculture
3. Mixed farming
4. Mediterranean agriculture
5. Commercial grain farming
6. Livestock ranching
7. Commercial gardening and fruit farming
8. Dairy farming
9. Grain farming
10. Shifting cultivation
11. Pastoral nomadism

5. Influence and Legacy:
D. Whittlesey's classification of agricultural regions has had a lasting impact on the field of agricultural geography. His work provided a framework for understanding the diversity of agricultural practices across the globe. Researchers and policymakers continue to use Whittlesey's classification system as a basis for studying agricultural regions and formulating agricultural policies.

In conclusion, D. Whittlesey was responsible for first delineating the major agricultural regions of the world. His classification system has been widely adopted and serves as a foundational framework for understanding agricultural practices and patterns globally.