Hi there.
I think the answer to your question is: nitrogen.
Nitrogen is found in proteins, but not carbs.
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A dichotomous key is two paired sentences that have contrasting characteristics. That's all i know
Answer:
The respiratory system works directly with the circulatory system to provide oxygen to the body. Oxygen taken in from the respiratory system moves into blood vessels that then circulate oxygen-rich blood to tissues and cells.
