— 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?

DNA双螺旋每旋转一周沿轴上升的高度是（）。

A．0.15nm

B．0.54nm

C．2nm

D．3.4nm

E．3.6nm