The correct answer is D. A big part of their economy depends on tourism, agriculture jobs, and the movement of goods.
The sun belt is constantly growing since it was in a very bad economic shape in the previous century. There is a lot of tourism in areas like Canada, Florida, Las Vegas, and there are a lot of agricultural jobs because of vast lands that have farms or ranches. Movement of goods is also important as the climate is good for transporting goods, especially since the invention of the air conditioning unit.