Mammals and Birds Have Four-Chambered Hearts and Fully Divided Pulmonary

Mammals and birds have four-chambered hearts and fully divided pulmonary and systemic circulations. The circulatory systems of reptiles and amphibians are sometimes presented as "inferior" because pulmonary and systemic circulations are not completely separate. What might be an advantage to incompletely separated circuits in these organisms?

A) Incompletely separated circuits take less energy to function.
B) In incompletely separated circuits, the distribution of blood flow can be adjusted, depending on whether or not the animal is breathing air through its lungs.
C) Incompletely separated circuits allow for higher blood pressure and therefore increased blood flow.