Ecological succession represents .........

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

$A$ food web:

Given below are four statements $(a-d)$ each with one or two blanks. Select the option which correctly fills the blanks in two statements.
$(a)$ Ecological succession is a ...$(i)$... and fairly predictable change in the ...$(ii)$... of a given area.
$(b)$ In ecological succession,the entire sequence of communities that successively change in a given area is called ...$(i)$....
$(c)$ Primary succession occurs on ...$(i)$....
$(d)$ Secondary succession is ...$(i)$... than primary succession.

Some of the stages in the hydrarch succession are labelled as:
$I.$ Marsh meadow stage
$II.$ Reed swamp stage
$III.$ Submerged plant stage
$IV.$ Phytoplankton stage
$V.$ Submerged free floating plant stage
Identify the choice that represents the correct sequence of these stages.

Which of the following contribute to the carbon cycle?