单选题 It can be inferred from Paragraph 1 that one important factor in the increasing importance of education in the United States was ______.

A、 the growing number of schools in frontier communities
B、 an increase in the number of trained teachers
C、 the expanding economic problems of schools
D、 the increased urbanization of the entire country

【正确答案】 D

【答案解析】[试题分析] 事实判断题。
[详细解答] 根据第一段第三句“Industrialization and the bureaucratization of economic life combined with a new emphasis upon credentials and expertise to make schooling increasingly important for economic and social mobility．”的内容，可以推断，显然D为正确答案。