I was giving a talk to a group of people.I

问题补充：

I was giving a talk to a group of people.I

答案：

填:had given

was giving 是过去动作,在此之前曾给其他几群人作过同样的报告,

故应用过去完成时.

句意:我当时正在给一群人作报告,在此之前我曾给其他几群人作过同样的报告