Only according to the directions can the medicine be quite effective.
A. taking
B. taken
C. being taken
D. having been taken
网友回答
A. taking
(答案→)B. taken
C. being taken
D. having been taken
解析：考查分词用法。Medicine与take之间构成被动关系，所以使用过去分词的形式，C表示正在被服用；D表示已经被服用；句意：只有根据说明书服用，这个要才相当有效。