Decomposers
a. make their own food
b. get energy directly from the sun
c. can be carnivores, omnivores, or herbivores
d. return essential chemicals to an ecosystem

The answer is D
Decomposers do not make their own food, they feed off of the remains of plants and animals
Decomposers also do not get energy from the sun, since their cells do not have chloroplasts which make chlorophyll for photosynthesis
Decomposers cannot be considered carnivores, omnivores or herbivores, since they are typically fungi and are not part of the animal kingdom.
Therefore, we know that decomposers return nutrients, such as nitrogen, carbon and phosphorus, back into the ecosystem through decomposition.