The Greatest Metabolic Advantage of a Fish's Two-Chambered Heart Is

The greatest metabolic advantage of a fish's two-chambered heart is

A) its ability to pump blood under high pressure to all areas of the fish's body.
B) its ability to pump blood to the gills for gas exchange before the blood is pumped to the remaining areas of the body.
C) its ability to stay full of blood even as it is emptying into the conus arteriosus.
D) its ability to keep oxygen-rich blood in one chamber separate from oxygen-poor blood in the other chamber.
E) its ability to maintain a constant blood pressure in the fish.