The correct option is A Homeostasis
Homeostasis is the tendency of the body to seek and maintain a condition of balance or equilibrium, maintaining parameters such as blood pressure, water content, temperature etc around a set point, in its internal environment, even when faced with external changes.
Ectotherm, also known as a poikilotherm, on the other hand is an animal that is dependent on external sources of body heat.
A homeobox is a DNA sequence, around 180 base pairs long, found within genes that are involved in the regulation of patterns of anatomical development (morphogenesis) in animals, fungi and plants.
And endotherms or homeotherms are organisms that maintain their body temperature at a constant level, usually above that of the environment, by its metabolic activity.