You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Like bacteria, archaeans are important decomposers. For example, archaeans help break down sewage in waste treatment plants. As decomposers, they help recycle carbon and nitrogen. Answer: decomposer
Output:
Archaeans help break down sewage in waste treatment plants, so they fulfill what important role?