问题
选择题
Only when___________ according to the directions can the medicine be quite effective.
A．taking
B．taken
C．being taken
D．having been taken
答案
答案：B
题目分析：句意：只有当按照说明被服用这个药才能非常有效。这里用了状语从句的省略，完整的是only when the medicine is taken according to the directions can…，当主从句的主语一致的时候，可以省略从句的主语和be动词，所以选B。
