I want you to think for just a minute about a building; your house or your school, for example. Many buildings are made of cement blocks or bricks. My body is made of millions of tiny blocks that get piled like bricks. We call each brick a cell.
Each cell needs air and food to let it live and grow. How does the food that we eat and the air that we breathe get to all these cells? It is carried in our blood.
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