The northern parts of the United States get very cold in the win

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_____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. 第（29）题答案
A、when
B、where
C、unless
D、though
【正确答案】：A
【题目解析】：在第29题中，我们需要选择一个合适的连词来连接句子中的两个部分：“It has become...for old people to move south to these places”和“they retire”。 A选项“when”表示当...时候，引导时间状语从句，符合句意，即“当老人退休的时候，他们迁移到南方这些地方已经成为了一种趋势”。 B选项“where”通常引导地点状语从句或定语从句，表示在...地方，但在此句中，并不适用，因为句子要表达的是时间关系，而不是地点关系。 C选项“unless”表示除非，如果不，用于引导条件状语从句，但在此句中，并不适用，因为句子并没有表达“如果不退休就不迁移”这样的条件关系。 D选项“though”表示尽管，虽然，用于引导让步状语从句，但在此句中，并不适用，因为句子并没有表达让步关系。 因此，根据句子的结构和语境，选择A选项“when”是最合适的。