Debating___ this question with his teacher,he learned a lot.
英语中当主句的主语(he)与从句的主语（he）相同,从句中又有be动词（was）时,可以略去从句的主语和be动词,还可以省去连词.
又如：When I am standing here,I am talking to you.
= Standing here,I am talking to you.