Given below are four statements $(a-d)$ each with one or two blanks. Select the options which is correctly fill up the blanks into two statements.

$(a)$ Ecological succession is a…$(i)$… and fairly predictable changes in the ….$(ii)$… of a given area

$(b)$ Ecological succession, entire sequence of communities that successively change in given area are called …$(i)$….

$(c)$ Primary succession occurs on…$(i)$…

$(d)$ Secondary succession is …$(i)$… than primary succession

Which one is not dangerous for life and atmosphere

The graph below shows the changes in two populations of herbivores in a grassy field. A possible reason for these changes is that

Secondary succession takes place on/in

Which of the following is present in maximum amount in atmosphere