Genetic drift operates only in

The given flow chart shows classification of acquired immunity. What types of immunity will be developed by the persons $\mathrm{X}$ and $\mathrm{Y} ?$

$\mathrm{X}:$ A person who has recovered from an attack of measles.
$\mathrm{Y}:$ A person who is given anti-tetanus serum.

The given table shows some information about the trophic levels of a food chain.

Select the option with correct order of trophic levels in a food chain.

The density of a population in a given habitat during a period, fluctuates due to changes in certain basic processes. On this basis, identify $\mathrm{A}$ and $\mathrm{B}$ boxes in the given flow chart.

In the given figure, identify the tropical forest and coniferous forest from the markings $\mathrm{A}-\mathrm{F}$ and select the correct option.

Examine the given figure and select the right option in which all the four structures $\mathrm{A}, \mathrm{B}, \mathrm{C}$ and $\mathrm{D}$ are labelled correctly.