1st answer to the question is A. Economic/industry factors
Explanation: The term "Rust Belt" refers to an economic region in the northeast United States, roughly covering the states of Michigan, Wisconsin, Indiana, Illinois, Ohio, and Pennsylvania, a region known as the manufacturing heartland of the nation.
2nd answer to the question is the explanation read it I hope it helped you to find the answer:)
Sun Belt, region comprising 15 southern states in the United States and extending from Virginia and Florida in the southeast through Nevada in the southwest, and also including southern California. Between 1970 and 1990, the South grew in population by 36 percent and the West by 51 percent, both well above the national average. Large in-migration, along with a high birth rate and a decline in out-migration, all contributed to rapid growth of both the Sun Belt’s population and manufacturing activities. Improvements in transportation and communications, abundant air conditioning in summer, and a favourable winter climate are attractive forces for retirees as well as workers.