求解答一段GRE阅读social structure was in fact so fluid-though recen

本句话里,两个破折号之间的句子为插入语,即：though recent statistics suggest a narrowing of economic opportunity as the latter half of the century progressed为插入语所以本句先撇掉插入语,先看句子即为：social structure was in fact so fluid that to talk about social classes at all requires the use of loose econmic categories such as rich,poor,and middle class,or eighteeth-century designations like "the better sort"翻译为：社会结构实际上是如此的复杂,以至于我们在谈到社会阶级的时候最终需要运用模糊的经济分类,比如贵族,穷人和中产阶级,或者像十八世纪“更好的类型”的指定。插入语翻译为：尽管近期的数据显示在后半世纪经济机会已经改进得狭窄。整个翻译为：社会结构实际上是如此的复杂（尽管近期的数据显示在后半世纪经济机会已经变得狭窄）,以至于我们在谈到社会阶级的时候最终需要运用模糊的经济分类,比如贵族,穷人和中产阶级,或者像十八世纪“更好的类型”的指定。