题目

下列物质之间如图中箭头方向，通过一步反应不能实现转化的是（   ） A . B . C . D . 答案：B _____ new cure for this disease that medical experts have recently developed proves to be ______ most effective, although it can not completely kill all the viruses. A. A; a        B. The; /             C. /; the                   D. A; the