* Heterotrophs are organisms that cannot produce their own food. They obtain nutrients by consuming other organisms. Decomposer fungi break down dead organisms (plants, animals, and their waste products) to obtain their energy and nutrients.

Let's break down why other options are incorrect:

* Autotrophs: These organisms can produce their own food through processes like photosynthesis (plants) or chemosynthesis (some bacteria).

* Producers: This term is often used interchangeably with autotrophs, referring to organisms that form the base of the food chain by creating organic matter from inorganic sources.

* Consumers: These are organisms that obtain their energy by eating other organisms. Decomposers are technically a type of consumer, but they are distinguished from other consumers (like herbivores and carnivores) because they break down dead organic matter.

Therefore, the best answer is heterotroph.