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What is the difference between an artery and a vein?

1 An artery carries blood away from the heart; a vein carries blood to the heart.
2 An artery is responsible for carrying blood; a vein is responsible for gas exchange.
3 An artery is responsible for gas exchange; a vein is responsible for carrying blood.
4 An artery carries blood to the heart; a vein carries blood away from the heart.