语法与词汇 When the prairies were being settled, undoubtedly, the good economic conditions of the 1950’s supported a growth in the population, but the expansion also derived from a trend toward earlier marriages and an increase in the average size of families.
【正确答案】 A
【答案解析】句意：大草原上有人定居之后，良好的经济环境毫无疑问支持着二十世纪五十年代人口的增长，但是这种增长也是由于早婚以及家庭平均成员的扩张。trend趋势，与tendency同义。directive指示，指令。因此，本题的正确答案为A。