The circulatory systems of land-dwelling vertebrates are composed of two pumping circuits: the systemic circulation, which is a lower-pressure circuit to the lung, and the pulmonary circulation, which is a higher-pressure circuit to the rest of the body.

A. Land vertebrates are bigger and require more tubing to reach all areas of the body.
B. The large decrease in blood pressure as blood moves through the lungs may prevent efficient circulation through the rest of the body.
C. The circuits increase the amount of surface area available for the diffusion of gases and nutrients in the body.
D. Blood is pumped to the lungs to be oxygenated before being pumped to the rest of the body.