It is called a double circulatory system because blood passes through the heart twice per circuit. The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart. The left pump sends the newly oxygenated blood around the body.
I believe the answer is plants make flowers to attract insects because, plants do nit store carbohydrates, meat does, and we cant use plants to create fossil fuel. The only plant fibers we use for clothing is cotton so that is very limited in the wide aspect of things.
