预真空和脉动真空压力蒸汽灭菌器多长时间进行一次BD测试()
A.每日
B.每周
C.每月
D.每季
E.每年
参考答案:A
33. --- How can you be late for such an important conference?
--- Sorry! But my flight was ______ by fog.
A.taken over
B.held up
C.turned down
D.handed out
红外光学系统的特点?