Identify the stage of hydrarch succession shown in the figure.

Which of the following statements is incorrect regarding the phosphorus cycle?

Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

In an ecosystem, which of the following statements is true regarding trophic levels?

Trees $\rightarrow$ Birds $\rightarrow$ Lice $\rightarrow$ Bacteria. Thus,the food chain is:

$A$: Estuary constitutes one of the most productive ecosystems.
$R$: It represents a transition zone between two populations of a species.