题目解析:
定位第4段简化句,分析:industrialization of book production proceeded more rapidly in the United States,原因有二(1)larger than in Britain ,(2)more sensitive to price than to quality,后面 because elite readers constituted a smaller proportion of book buyers 作为(2)的原因。
选项 A 的 were similar inquality,选项 B 的 than is usually realized,选项 D 的 not as sensitive to quality as 均未提及,错误;
选项 C 符合原文主干及原因(1)(2)。
故选 C