In What Way Do Fungal Decomposers Contribute to Earth's Carbon

In what way do fungal decomposers contribute to Earth's carbon cycle?

A) They use CO₂ during photosynthesis.
B) They sequester carbon on the forest floor preventing it from entering the atmosphere.
C) They return carbon atoms to the atmosphere in the form of respiratory CO₂.
D) Fungal decomposers aren't involved in Earth's carbon cycle.
E) Both a and b