Which correctly list the three gases that each make up less than 1 percent of Earth’s atmosphere?

Nitrogen and oxygen make up most of Earth’s atmosphere, so choices A, C, and D include gases that are not below 1%. Argon and carbon dioxide are present in small amounts, and water vapor is also treated as a minor, variable component in this comparison. Thus, “argon, water vapor, carbon dioxide” is the correct choice. Water vapor can exceed 1% in humid air, so its exact amount varies by place and time.

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