根据以下材料，回答21-35题
The northern parts of the 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 commtmities 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．
第35题的答案是(　　)

A have opened  

B closed     

C rebuilt   

D setup