The northern parts of United States get very cold in the winter. It snows a great deal and the temperature often goes_____（21）zero degree in January, _____（22）and March. But the northeastern and northcentral regions of_____（23）have been financial and industrial centers, and they are heavily polluted.In recent years, people in these regions have begun to take vacations_____（24）these cold winter months They go to southern parts of the country_____（25）it is warmer. Many go to Florida where the weather is_____（26）.Others go to the southwestern states of Arizona, New Mexico and Texas where they_____（27）dry desert climates.It has become_____（28）nowadays for old people to move south to these places_____（29）they retire. Typically these people sell their houses in their home communities and move south to begin a new life_____（30）senior citizens.Their children likely have homes_____（31）and many of them are moving south_____（32）communities where they were_____（33）.The southern and southwestern parts of the country are now growing_____（34）any other part. Business and industry_____（35）many offices and factories in the south. California is already the most popular state in the country.

33_____.