The human body is amazing. Your blood makes up about 8% of your body weight. On average, your heart will beat more than 3 billion times in your lifetime! Doctors and scientists make choices every day about how to keep our bodies going. But what would you change if you could? Would you choose to have super strength or super speed? Would you rather have no bones or no muscles? It's your turn to pick this or that! Part of the This or That?: Science Edition series.