Why is the oxygenated blood that reaches the body cells of a fish generally at lower pressure than in a mammal? Select one: a. The fish’s blood is harder to pump because it is typically colder than its environment. b. The fish’s blood does not return to the heart after acquiring O2 in the capillaries of the gills. c. The fish’s heart does not have a ventricle. d. The fish’s blood is easier to pump because fish live underwater.