The correct response is that detritivores feed on dead organic matter, while decomposers break down that organic matter into simpler substances. Detritivores are typically larger organisms, such as earthworms and some insects, that ingest organic material, whereas decomposers, like fungi and bacteria, chemically break down organic matter at the microscopic level.
So, if you're looking for a more complete statement: "While detritivores feed on dead organic matter, decomposers break down that organic matter into simpler substances."