The Earth's Atmosphere, Which We Refer to as Air, Is $78 \%$

Multiple Choice

The earth's atmosphere, which we refer to as air, is a mixture of approximately

A) $78 \%$ oxygen, $21 \%$ nitrogen, and less than $1 \%$ carbon dioxide.
B) $78 \%$ nitrogen, $21 \%$ oxygen, and less than $1 \%$ argon.
C) $78 \%$ oxygen, $21 \%$ carbon dioxide, and less than $1 \%$ helium.
D) $78 \%$ oxygen, $21 \%$ water vapor, and less than $1 \%$ ozone.