$A$ regulators are able to maintain homeostasis by means which ensure constant body temperature,constant osmotic concentration,etc. All $B$ and $C$ and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation).
Evolutionary biologists believe that the 'success' of mammals is largely due to their ability to maintain a constant body $D$ and thrive whether they live in Antarctica or in the Sahara desert.
Choose the correct option for $A, B, C$ and $D$.

• A
  $A-$Behavioural,$B-$vertebrates,$C-$invertebrates,$D-$temperature
• B
  $A-$Behavioural,$B-$bird,$C-$mammals,$D-$temperature
• C
  $A-$Physiological,$B-$bird,$C-$mammals,$D-$temperature
• D
  $A-$Behavioural,$B-$vertebrates,$C-$invertebrates,$D-$morphology