Unlike amphibians, reptiles
a. have lungs to oxygenate blood. b. use single-loop circulatory system. c. have a closed circulation system in which blood circulates entirely within blood vessels. d. have ventricles that are further divided to lessen mixing of oxygen-rich and oxygen-poor blood.

The answer is D. have ventricles that are further divided to lessen mixing of oxygen-rich and oxygen-poor blood.

Amphibian hearts have 3 chambers - one ventricle and two atria. Since there is only one ventricle, oxygenated and deoxygenated blood will mix. On the other hand, lizards have a septum in the ventricle. The septum divides ventricles resulting in less mixing of oxygen-rich and oxygen-poor blood. 

Bis the correct answer.