Carbon dioxide and water vapor are variable gases because

a. heir amounts vary throughout the atmosphere.
b. they only make up 1% of the atmosphere
c. sometimes they're in the atmosphere, sometimes they're not
d. one gas depends on the other gas

A. their amounts vary throughout the atmosphere

Explanation:

Atmosphere consists of number of gases and composition of atmosphere varies depending on the amount of gases present in the atmosphere. The percentage of carbon dioxide in atmosphere is 0.04% while that of water vapors is 4% at normal room temperature.

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