The answer is (1) decomposer.
(2): Herbivores are animals that consume plants, such as rabbits or deer.
(3): Producers are usually the plants in an ecosystem.
(4): Scavengers are animals that feed off of the remains of other animals already killed by something else (like how a vulture will eat the meat off of dead gazelles after a lion finishes)
(1) decomposer is correct because bacteria and fungi often slowly consume or decompose dead organic material from plants and animals from the ecosystem.
