— He’s never stolen anything before，______ he?

—______ ．It’s his third time to be taken to the police station．

A．hasn’t：Yes

B．is；Yes

C．has；Yes

D．has；No

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