英语语法,非谓语动词上的问题whenaskedtocomparetheeducationsystemsofchinaandbritain,theprofessorgavehisowncomment这里为什么要用“askedtocompare”而不是“askedhimtocompare”?

Question

英语语法,非谓语动词上的问题
when asked to compare the education systems of china and britain,the professor gave his own comment
这里为什么要用“asked to compare”而不是“asked him to compare”?

Answer 1

when （he was） asked to compare the education systems of china and Britain,the professor gave his own comment.
省略了he was