Assertion: Smaller the organism higher is the rate of metabolism per gram weight.
Reason: The heart rate of a six-month-old baby is much lower than that of an old person.
A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false