— Jack, where is Tom?   

— He is in Mr. Smith's office now, sir.  

— Please tell him that I want to see her ______ she arrives.    [      ]

A. at the moment      

B. the moment  

C. in the moment    

D. For the moment

下列密封形式哪种属于动密封（）。

A、填料密封

B、垫片密封

C、螺纹密封

D、活接密封