Surface water of lake enrich in having

Which of the following isolation is important for speciation

Even a plant species, which makes its own food, cannot survive alone; it needs soil microbes to breakdown the …$A$… matter in soil and return the …$B$…. nutrients for absorption. And then, how will the plant manage pollination without an animal agent? It is obvious that in nature, animals, plants and microbes cannot live in …$C$… but interact in various ways to form a biological community

Choose the correct option for $A, B$ and $C$

Water logging occurs in

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