Secondary producers are

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

Assertion $A$: As a result of evolution,plant species have migrated from aquatic habitats to terrestrial habitats.
Reason $R$: Plants have undergone developmental changes while passing through various stages of succession.
Which option is correct for Assertion $A$ and Reason $R$?

In a food chain, which of the following is produced in the largest amount?

Identify the correct type of food chain.
Dead animal $\rightarrow$ Blow fly maggots $\rightarrow$ Common frog $\rightarrow$ Snake

Consider the following statements concerning food chains.
$A.$ Removal of $80\%$ tigers from an area resulted in greatly increased growth of vegetation.
$B.$ Removal of most of the carnivores resulted in an increased population of deers.
$C.$ The length of food chains is generally limited to $3-4$ trophic levels due to energy loss.
$D.$ The length of food chains may vary from $2$ to $8$ trophic levels.
Which two of the above statements are correct?