Question

what is the function of the part of decomposing mushrooms that grow below the ground?
photosynthesis with sunlight
decomposition of organic matter
attraction of pollinators

Explanation:

Mushrooms are decomposers. The part below - ground helps break down organic matter in soil. They don't perform photosynthesis as they lack chlorophyll, and attracting pollinators is not their underground function.

Answer:

decomposition of organic matter