喉挫伤是（）。
A.开放性喉外伤
B.闭合性喉外伤
C.喉内部外伤
D.贯通性喉外伤
E.喉插管损伤
参考答案：B
You ____ him so closely; you should have kept your distance.
A．shouldn't follow
B．mustn't follow
C．couldn't have been following
D．shouldn't have been following
能直接转变生成dUDP的化合物是( )
A．UTP
B．UDP
C．UMP
D．IMP
E．dUMP
