The correct answer that highlights an advantage of being an ectotherm is:
a) Ectothermy uses little energy to maintain metabolic rate.
Ectotherms, such as reptiles and amphibians, regulate their body temperature primarily through external means rather than metabolic heat. This means they typically require less energy to regulate their internal temperature, allowing them to be more energy-efficient compared to endotherms (like mammals and birds) who must produce sufficient metabolic heat to maintain a constant body temperature regardless of the external environment. This energy efficiency allows ectotherms to survive on less food and energy compared to endotherms.