问题
单项选择题
After each reading of an oxygen indicator，the instrument should be purged with（）.
A.CO2
B.fresh air
C.the tested compartment's air
D.water
答案
参考答案：B
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After each reading of an oxygen indicator，the instrument should be purged with（）.
A.CO2
B.fresh air
C.the tested compartment's air
D.water
参考答案：B