Answer:
The correct answer is A. breaking down organic matter
Step-by-step explanation:
Bacteria and archaea are the domains that come under prokaryotes. These organisms lack nucleus. They play an important role in the nutrient cycle. Most of these organisms are heterotrophs and consume organic matter to gain energy.
They play an important role in breaking down the organic matter and releasing the nutrient from them in the environment so they helps in circulating the nutrients in the ecosystem.
For example, different methanogens and acid-forming bacteria decompose organic waste of industry and agriculture and produce manure and biogas during anaerobic decomposition. So the correct answer is A.