Correct answer: C). They convert dead organic compounds into reusable organic compounds.
The main aim of decomposers is to degrade the complex dead and organic matter present in the environment into simple reusable compounds, which can easily enter into the soil and make them fertile, and these are again available for use by the producers.
They free up physical space by degrading dead remains of plants and animals and make nutrients available for use again and again.
Hence, the correct answer would be option C.