Why does the heart automatically adjust the flow of blood to match activity levels?

The reason is because the heart requires more oxygen when exercising. Several physiological events happen to increase the blood flow and therefore oxygen flow to that muscles,including the heart.

Also the volume of blood that the heart pumps out is maintained so that the body organs receive the necessary amount of oxygen and nutrition, because if it didn't adjust the flow of blood to match activity level, you will be insufficient. Either output method will be lower than needed.

B) The heart requires more oxygen when exercising.

answer: proteins

explanation: complement is   system of circulate in the blood in a inactive form

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it hurts at first because " the cherry is broken" which is a thin layer of skin that breaks so the first time girls have sex it hurts and it bleeds but after the first time it does hurt again because the skin that ia torn does not break again/ grow back.