白勇语法关于比较从句的省略: 有这么一条:“.比较从句的主语和位于与主句的主语和谓语相同时,可以全部省去,常常保留作状语的介词短语或状语从句。” 但是有一题PREP: 原题:To develop more accurate population forecasts, demographers have to know a great deal more than they do now about the social and economic determinants of fertility.(正确选项) 一个选项是have to know a great deal more than now about the social and economic(X) 这个选项不能算是上述所说的那种省略吗?