The correct answer is: a) River deltas.
River deltas are areas of land that are formed where a river meets the ocean. They are typically very fertile and well-suited for agriculture. However, they are also prone to flooding, which can damage crops and infrastructure.
Dry interior regions are areas that are located far from the coast and do not receive much rainfall. They are typically very dry and arid, and agriculture is difficult to sustain without irrigation.
Coastal areas are areas that are located near the ocean. They are typically very humid and have a lot of rainfall. However, they are also prone to storms and hurricanes, which can damage crops and infrastructure.
Hilly areas are areas that are characterized by steep slopes. They are typically not well-suited for agriculture, as the slopes make it difficult to plow and plant crops.
In conclusion, river deltas are the areas where the availability of irrigation water is a major determinant of cropping patterns.