$A$… regulators are able to maintain homeostasis by means which ensures constant body temperature, constant osmotic concentration, etc. All …$B$… and …$C$…. and is 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 $D$

Photosynthesis in Opuntia is done by

They are dominant plants of the cold desert

When young plants are grazed too heavily, they get killed because of