What is the primary succession in freshwater called?

Broad-leaved forests of oak are found in

The following diagram shows the phosphorus cycle. Identify the producers in it.

Phosphorus of the ocean becomes available to land plants due to:

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

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?