The correct answer is:
a. It causes mixing of oxygenated (blood with oxygen in it) and deoxygenated blood (blood without oxygen in it), making it harder for the body to get the oxygen it needs.
In a frog's heart, which has only one ventricle, oxygenated and deoxygenated blood can mix, resulting in less efficient oxygen delivery to the body compared to a circulatory system with separate ventricles (as in mammals).