下列物质中不是空气固有成分的是 [ ]
A.氧气
B.氮气
C.二氧化硫
D.稀有气体
答案:C
— Someone is knocking at the door. Who _____ it be?
— It must be the milkman. [ ]
A. may
B. must
C. can
D. need
在电气设备中6,就吸附原理来说,SF分解物在固体表面的吸附有()。
A.物理吸附
B.化学吸附
C.静态吸附
D.动态吸附