When ( ) the education systems of China and Britain ,the professor gave no comment.

题目

When ( ) the education systems of China and Britain ,the professor gave no comment.
A asked him to compare
B asked to cpmpare
A和B搞不明白啊

答案

When asked to cpmpare the education systems of China and Britain ,the professor gave no comment.
（当教授被要求比较中英的教育制度时,他没有给出意见）.主语是教授
这里是考察非谓语动词不定式作宾语补足语.
When asked to compare = When the professor was asked to compare（这里的谓语是作为被动语态).
A答案asked him to compare不为被动语态