In the carbon cycle, decomposers break down dead material from plants and other organisms and release carbon dioxide into the atmosphere, where it's available to plants for photosynthesis, so your answer would be the first one!
The answer is 'They release the carbon that remains in the bodies of dead organisms'.
Decomposers are heterotrophic organisms which get their nutrition by breaking down remains of dead plants and animals. The process of breaking down the dead remains of plants and animals is termed as decomposition. They help in recycling of the nutrients such as carbon and nitrogen in an ecosystem. They return these nutrients to the soil from where plants can reuse the same.
