Think about the human body: It wouldn't work without the brain. It wouldn't function without the heart. And the lungs are super important too! In this silly set, readers consider several science topics and try to decide which part of the whole matters most--from the sun to coal, from gravity to friction. Illustrated characters guide readers throughout the series, adding facts and fun along the way. Each book concludes with an answer to what matters most--but the emphasis is on the importance of variety and parts to the whole.