Which of the following levels is not considered a biological level of organization in terms of size?

$A$ characteristic which enables an organism to live in an environment is called

$A$ 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 $D$.

What is a tree line?

$A$ group of two or more than two plant species is called as

How is a biological community formed?