Final answer:
Smaller endothermic animals have a greater surface area for their mass compared to larger endothermic animals.
Step-by-step explanation:
Smaller endothermic animals have a greater surface area for their mass compared with larger endothermic animals. This means that their body surface to body mass ratio is higher than that of larger animals. As a result, smaller animals lose heat at a faster rate and require more energy to maintain a constant internal temperature.
For example, imagine two endothermic animals, one small and one large. The smaller animal will have a relatively larger body surface area compared to its mass, while the larger animal will have a relatively smaller body surface area in proportion to its mass. This higher surface area in smaller animals allows for more heat loss, which necessitates a higher basal metabolic rate (BMR) to compensate for the increased heat loss and maintain a constant temperature.
The correct option is A.