Final answer:
The easiest way for poikilothermic or ectothermic animals, such as lizards, to regulate body temperature is through behavioral thermoregulation, such as basking in the sun or seeking shade. The correct option is d).
Step-by-step explanation:
For most poikilothermic or ectothermic animals, such as lizards, the easiest way to regulate body temperature is through behavioral thermoregulation.
These animals do not have the ability to sweat, pant, or shiver effectively as a means of controlling their body temperature. Instead, they rely on behaviors like basking in the sun to warm up or seeking shade to cool down.
In deceptively simple ways, by moving between places with different temperatures or by altering their exposure to the sun's radiation, they maintain an optimal body temperature for functioning.
Examples of behavioral thermoregulation include reptiles like lizards climbing onto rocks to absorb heat or finding shade under vegetation to stay cool.
As ectotherms depend largely on environmental temperatures to dictate their internal temperature, these behavioral strategies are crucial for their survival and are more energy-efficient compared to physiological responses such as sweating or shivering that endotherms might use. Option d) is the correct one.