91．The agricultural revolution stimulated many in the countryside toseek a new life in the city and made it possible for fewer farmers to feed thelarge concentrations of people needed to provide a workforce for growingnumbers of factories．

(and连接的并列句；过去分词结构needed to…作large concentrations of people的定语)

农业革命刺激了许多生活在乡村的人去城市寻找新生活，而且使较少的农民有可能养活不断增加的工厂需要用来提供劳动力的集中人群。

分句1：The agricultural revolutionstimulated many in the countryside

分句2：to seek a new life in the city

分句3：made it possible for fewer farmers

分句4：to feed the large concentrations ofpeople

分句5：needed to provide a workforce forgrowing numbers of factories．

1和2嵌套

3和4嵌套

4和5嵌套，5修饰4中的the large concentrations of people

1和3并列