【名词&注释】
低温泵(cryopump)、离心式(centrifugal)
[单选题]离心式低温液体泵多采用充气迷宫密封,密封气为(),气体压力要高出低温泵的叶轮背压()左右
A. 氧气,0.02MPa B. 仪表空气,0.01MPa C. 仪表空气,0.02MPa D. 高压氮气,0.01MPa