Which ecosystem is more stable?

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?

What is true about the phosphorus cycle?
$I.$ Rocks are the natural reservoirs of phosphorus.
$II.$ Weathering of sedimentary rocks makes phosphate available to the soil.
$III.$ Herbivores and carnivores obtain phosphorus from plants directly or indirectly.
Choose the correct option.

Complete the following model of the carbon cycle by filling in $A, B, C, D, E,$ and $F$.

Which of the following is $NOT$ a gaseous biogeochemical cycle in an ecosystem?

Which one of the following is not a function of an ecosystem?