The answer is D. The question asks how different cultures influenced each other so that rules out options A & B. Option C is about the environment being destroyed, and that really has nothing to do with foreign influence.
As the agriculture's are used to villages life and have to take care of the larger tracks of the lands and they thus live close by as compared to the semi-permanent horticulturalists.
As horticulture is not a permanent type of occupation and they don't need to bee close to the farms and required less maintenance.
