Which of the following is NOT a form of thermal regulation?

Thermal regulation refers to the processes that organisms use to maintain their internal body temperature within a certain range, despite external temperature changes. Among the options listed, respiration is not primarily a method for heat exchange or thermal regulation. While respiration involves gas exchange and does produce some heat as a byproduct, it is not a direct mechanism through which organisms regulate their body temperature.

In contrast, conduction, evaporation, and radiation are all physical processes through which heat can be transferred in relation to an organism's environment. Conduction involves direct heat transfer through contact with another substance, evaporative cooling helps organisms lose heat through the conversion of liquid to vapor, and radiation entails heat transfer through electromagnetic waves. Each of these plays an essential role in how organisms manage their thermal balance, particularly in varying environmental conditions.