Many freshwater fishes cannot live in seawater and vice versa because of:

Altitude sickness is an example of:

$A$: Antarctic fishes have blubber to withstand sub-zero temperatures.
$R$: Blubber are proteins which allow the freezing of body fluids.

Which of the following is a characteristic of a biological community?

Read the following statements and select the option that represents the correct statements.
$(1)$ Kangaroo rats never drink water.
$(2)$ Birds undergo hibernation to escape adverse environmental conditions.
$(3)$ Thermal adaptation can be explained by Allen's Rule.
$(4)$ Opuntia possesses phylloclade for protection.

Do you agree that regional and local variations exist within each biome? Substantiate your answer with suitable examples.