Identify the possible link $A$ in the following food chain.
Plant $\rightarrow$ Insect $\rightarrow$ Frog $\rightarrow$ $A$ $\rightarrow$ Eagle

Identify the possible link '$M$' in the following food chain.
Plant $\rightarrow$ Insect $\rightarrow$ $M$ $\rightarrow$ Snake $\rightarrow$ Eagle

In the carbon cycle,the source of carbon for plants is:

Match the columns:

Column-$I$	Column-$II$
$(i)$ Primary succession	$(i)$ Development of ecosystem
$(ii)$ Ecological succession	$(ii)$ Lichens
$(iii)$ Pioneer species on rocks	$(iii)$ Near to the equilibrium with the environment
$(iv)$ Climax community	$(iv)$ New species on bare environment

Consider the following statements about food chain:
$I.$ The transfer of energy from producers to top consumers through a series of organisms is called a food chain.
$II.$ $A$ food chain is always straight and proceeds in a progressive straight line.
$III.$ In a food chain,there is a unidirectional flow of energy from the sun to producers and subsequently to a series of different types of consumers.
Which of the statements given above are correct?

Which of the following statements regarding food chains are considered correct?
$(1)$ Removal of $80\%$ of tigers from an area results in greatly increased growth of vegetation.
$(2)$ Removal of most carnivores results in an increased population of deer.
$(3)$ The length of food chains is generally limited to $3-4$ trophic levels due to energy loss.
$(4)$ The length of food chains can vary from $2$ to $8$ trophic levels.