Generally speaking according to the directions the drug has no side effect .A. when ta

问题补充：

Generally speaking , according to the directions , the drug has no side effect .

A. when taking

B. when taken

C. when to take

D. when to be taken

答案：

A. when taking

(答案→)B. when taken

C. when to take

D. when to be taken

解析：当分词的逻辑主语也就是主句的主语，这时可以省去逻辑主语和be动词.现在分词表示主动和进行，而过去分词表示被动和完成。在这个句子中，其实是when the drug is taken,省去了the drug is，the drug 和take是被动关系．