Which of the following gases is normally not present in air?

问题描述：

Which of the following gases is normally not present in air?
A.Oxygen B.Hydrogen
C.Nitrogen D.Carbon Dioxide
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To myth2000:Sorry but one answer is too little for me..lets wait for another answer.

1个回答分类：英语 2014-11-17

问题解答：

我来补答

B
Normally,the air is combined by 20.25% Oxygen(A),78% Nitrogen (B),0.03% Carbon Dioxide (D) and some other rare gases.
Anyway Hydrogen (B) is also one of the components of air,but the content is very very low.

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