A stands out most to me, CO comes from the air and air is basically oxygen we breath. When we exhale CO comes out (of course). I would say A is correct.
Histamines are chemicals released by the body as an allergic response.They help the body by reacting when their are "intruders" so when enters, histamine acts as a messenger and sends out a signal for the body to create a reaction helping to get rid of teh intruder through some type of reaction.
Answer:
O proteins
Hope it helps
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