Planet a is an inner planet with no moon and hardly any atmosphere. planet b is an inner planet with no moon but with a dense atmosphere. which pair of planets is being described?

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There are two inner planets that have no moon. Mercury, and Venus. Only Mercury has hardly any atmosphere. Therefore, Planet A is Mercury. Venus which is composed primarily of carbon dioxide with a small amount of nitrogen is considered a planet with a dense atmosphere. Therefore, Planet B is Venus.

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