We were talking and laughing, when our teacher came in and asked us what all the  ______  was about.

A．excite

B．exciting

C．excited

D．excitement

在金属表面上形成能抑制金属溶解过程的电子导体膜，而这层膜本身在介质中的溶解速度又很小，以致它能使金属的阳极溶解速度保持在很小的数值上，则这层表面膜称为（）

A.预膜

B.钝化膜