Assertion: Warm-blooded animals have their left and right side of the heart separated for more efficient supply of oxygen to the body.
Reason: Warm-blooded animals need high energy to maintain their body temperatures.
(1)
Warm-blooded animals need high energy to maintain their body temperature and thus their left and right side of the heart are separated for more efficient supply of oxygen to the body. Thus, both assertion and reason are correct and reason is the correct explanation of the assertion.