Concept:Saprophytism is a feeding relationship in which only one organism, the saprophyte, is directly involved.Explanation:Saprophytes obtain energy from dead and decaying organic matter such as plant litter or animal remains.They do not interact with a living partner in the process.Commensalism, parasitism, and symbiosis all require at least two different organisms living in relationship.Since saprophytism involves only a single organism acting on dead material, it is the correct answer.Answer:A. Saprophytism