19. Comparing the circulatory systems of vertebrates, which statement regarding "double circulation" is CORRECT? (A) In amphibians, oxygen-poor blood flows through the pulmonary circuit only. (B) In reptiles, a complete septum always divides the ventricle into two separate chambers. (C) Double circulation maintains lower blood pressure in the organs compared to single circulation. (D) In amphibians, the pulmocutaneous circuit allows for gas exchange through both the lungs and the skin.