B. Decayed matter - earthworm-duck
The answer is b. I am not sure exactly how to explain this, but it fits in much better with that question. I hope this could help you!
Answer: They can be either of the same species (intraspecific interactions), or of different species (interspecific interactions). These effects may be short-term, like pollination and predation, or long-term; both often strongly influence the evolution of the species involved. A long-term interaction is called a symbiosis.
Explanation:
True, a vast, flat, treeless Arctic region of Europe, Asia, and North America in which the subsoil is permanently frozen.