what type of circulation is described as the movement of blood from the heart to the lungs and back to the heart again? a. portal b. pulmonary c. renal d. systemic user: which statement explains why the pulmonary artery splits into two branches? a. because the heart has two halves b. because the pulmonary artery goes to two lungs c. because the pulmonary vein has two functions d. because the right ventricle connects two chambers ...