Answer:
D. whether regions characterized by harsh climates are likely to experience population declines in the foreseeable future
Step-by-step explanation:
Both Paul and Diana talk about regions with harsh climate conditions. Meanwhile, Diana says that they will experience a decline in population because elderly people will move from to the regions with a more temperate climate. At the same time, Paul talks about another consideration important to the elderly people - cost of living. He says that regions with harsh climate are cheaper to live in and thus more attractive for elderly people.
Thus, point of disagreement between Diane and Paul is about the probability that regions with harsh climate will have a population decline in the future.