D. The octupus population would decrease.
This is because if more sharks were in the ecosystem than they would feed on more octopus, decreasing the population of them.
The right answer is C
This process is called anaerobic respiration. It doesn't need dioxygen to occur (it can happen with or without O2).
Anaerobic respiration is a mechanism in which electrons pass through a chain of transporters whose final acceptor is a mineral substance other than oxygen, unlike aerobic respiration where the final acceptor is dioxygen. The final acceptor may be the nitrate ion (as in the case of Pseudomonas), carbon dioxyde or the sulfate ion.
Some bacteria (Pseudomonas) are able, anaerobically, to reduce nitrates to nitrites and then, depending on the case, to dinitrogen (with the enzyme Nitrate reductase A).
NO3- ==> NO2- ==> N2.
It's B, Most them can make or produce their own food.
