Answer
a.
Work Step by Step
Option b. is incorrect. Ectothermy is a characteristic of organisms whose internal temperature is governed by the temperature of their external environments.
Option c. is incorrect. Endothermy is the ability of an organism to control its internal body temperature despite the temperature of the external environment.
Option d. is incorrect. Reactivity happens when an organism responds to a stimulus.
Option a. is correct. Homeostasis is the process of maintaining a constant internal environment within an organism.
