All those second - hand books are sold at _____ before

题目

All those second - hand books are sold at _____ before
A.twice as a lower price as B.as twice low price than
C.twice as low a price as D.twice lower price than
这道题应该选什么呢,好像没有一个符合倍数表达法的,其他的几个错误选项应该怎么改才正确呢,望英语考试赐教

答案