Although everything seems to have been taken into consideration, ______ accident can happen when

the astronauts walk in ______ space. [ ]

A. /; the

B. an; the

C. the; the

D. an; /

常规CT扫描采取俯卧位的是（）。

A.头颅轴扫

B.双膝轴扫

C.双踝轴扫

D.双腕轴扫

E.双髋轴扫