—  I think you'd better type this letter again before Mr. Smith see it.  

— Oh, dear!           [ ]

A. Who cares?  

B. No problem    

C. I don't mind at all    

D. Is it as bad as that?

闸阀具有（）、启闭力较小、燃气可反向流动等优点。

A、阻力大

B、阻力小

C、无阻力

D、阻力损失小