Answer:
They can be found in several trophic levels, as they are related with several trophic level, hence, they cannot be placed on a specific trophic level.
Step-by-step explanation:
A trophic level is a specific position occupied by a group of organisms on a good chain in relation to their nutrition.
Dentrivores feed on the waste of other organisms and cannot be really placed on a specific trophic level, likewise decomposers, of which they feed and decompose the body of organisms.
Omnivores feed on both plants and animals, which includes producers and consumers. Placing omnivores on a specific trophic level would not be really straightforward also.