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"1) In one part does an air enter firts? 2) Where does the exchange of oxygen and carbon dioxide take palce? 3)Why does a person need oxyg
"1) In one part does an air enter firts? 2) Where does the exchange of oxygen and carbon dioxide take palce? 3)Why does a person need oxygen? 4) Which is the main part of circulatory system? 5)Why does the heart need to pump the blood?" | |
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