The given food web contains some missing organisms $A, B, C$ and $D$. Identify these organisms and select the correct answer.

Which of the following is an example of a man-made ecosystem?

Arrange the stages of hydrarch succession in the correct sequence.

Time is a crucial factor for . . . . . . .

The components of an ecosystem include .......... .

Consider the following four statements $(A-D)$ and select the correct option stating which ones are true $(T)$ and which ones are false $(F)$.
Statements:
$(A)$ Vertical distribution of different species occupying different levels in a community is called stratification.
$(B)$ Net primary productivity minus respiration losses is the gross primary productivity.
$(C)$ Rate of biomass production is called decomposition.
$(D)$ Annual net primary productivity of oceans is $55$ billion tons.