In the oxygen–carbon dioxide cycle, a. animals produce oxygen used by plants for photosynthesis.
b. animals produce oxygen used by plants for respiration.
c. animals produce carbon dioxide used by plants for photosynthesis.
d. animals produce carbon dioxide used by plants for respiration.

C

Explanation:

Animals produce carbon dioxide as a byproduct of cellular respiration. Plants use the carbon dioxide through photosynthesis to produce oxygen.

the correct answer is d

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these macromolecules could either be amino acids, proteins or nucleic acids. they are responsible for the chemical changes and reactions that affects largely the cell and its composition. take for instance the cytoplasm of the cell where these organelles are settled. these simple organelles are composed of macromolecules which ignites and catalyses different functions that enables cells, in macro-perspective in motion and metabolism. in intestines for example, metabolism happens and breaking down parts of a food to simpler compounds that are used and these nutrients delivered throughout the body and again broken down by into smaller components.