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