Generally speaking acording to the
instructions，the drug has no side effect.
A. when taking
B. when taken
C. when to take
D. when to be taken
网友回答
A. when taking
(答案→)B. when taken
C. when to take
D. when to be taken
解析：B 完整的说法应是when the drug is taken according to the directions，…。由于主句的主语和从句的主语相同，且从句中的谓语动词含有be的某种形式，因此可以省略从句的主语the drug和is。