A combination combustible gas and oxygen indicator is an instrument that measures the_____

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A combination combustible gas and oxygen indicator is an instrument that measures the_____ of both combustible gas and oxygen; each is indicated on a separate meter.

A.purifies

B.combinations

C.concentrations

D.filters

请帮忙给出正确答案和分析,谢谢!

热搜:a是b的充分条件,b是a的必要条件吗