Answer:
i think Decaying plant matter is answer
High concentration and passive transport
The end products are also different, in every living organism water and carbon dioxide are produced in aerobic respiration, whereas in anaerobic respiration, animals produce lactic acid, while plants and micro-organisms produce ethanol.
It is A. Those are all decomposers, the other answers like C are all animals. Decomposers are are biotic organisms that break down basically dead plants or animals.