You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

What is a primary role of decomposers in an ecosystem?
(A) They eliminate matter by taking nitrogen from the ecosystem. (B) They eliminate matter by taking phosphorus from the ecosystem. (C) They cycle matter by returning carbon and other matter to the ecosystem. (D) They cycle matter by returning oxygen and other matter to the ecosystem.
C