—Did you return the book on me? Why can’t I find it anywhere?

—_______. You were writing a letter at your desk at that time.

A．I will give it to you

B．I did give it to you

C．I had given it to you

D．I do give it to you

干气密封适合于（）。

A.级间密封

B.轴端密封

C.密封液气

D.密封气体