What type of human population is represented by the given age pyramid?

$A$ country with a high rate of population growth took measures to reduce it. The figure below shows age-sex pyramids of populations $A$ and $B$ twenty years apart. Select the correct interpretation about them.

Which of the following statements is correct?
$I.$ In a population,birth rate and death rate refer to per capita births and deaths,respectively.
$II.$ In nature,we rarely find isolated single individuals of any species.
$III.$ The size of a population for any species is a stable phenomenon.
$IV.$ Ecological effects of any factors on population growth are generally reflected in its size/population density.

Death is important because it ......

Identify $X$ and $Y$ in the given figure,which represents the biome distribution with respect to mean annual temperature and mean annual precipitation.

Which process allows organisms to protect themselves during stressful environmental conditions?