Question

which statement describes an important role of carbon dioxide in earths atmosphere?
animals breathe carbon dioxide.
plants use carbon dioxide to make food.
carbon dioxide helps animals make proteins.
carbon dioxide forms clouds that produce rain.

Explanation:

Plants perform photosynthesis, using carbon dioxide ($\ce{CO2}$), water ($\ce{H2O}$), and sunlight to produce glucose (food for the plant) and oxygen ($\ce{O2}$). The chemical equation for photosynthesis is $$6\ce{CO2}+6\ce{H2O}\xrightarrow{\text{sunlight}} \ce{C6H12O6}+6\ce{O2}$$. Animals breathe oxygen, not carbon dioxide. Nitrogen (in the form of nitrates etc.) is more relevant for protein synthesis in animals (as proteins contain nitrogen). Clouds are mainly formed from water vapor condensing, not carbon dioxide.

Answer:

Plants use carbon dioxide to make food.