—You've left the light on.

—Oh.So I have.________and turn it off.

A．I'll go

B．I've gone

C．I go

D．I'm going

螺纹标记B80×10表示公称直径d为80mm，螺距P为10mm的( )螺纹。

A．梯形

B．矩形

C．锯齿形