Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Any organic material can be made into electricity. But some materials are better than others. Wastes can be used, like almond shells. Biomass power is a great use of wastes. It's hard to use wastes as a consistent large scale source of energy though. Answer: organic waste
A:
What kind of material that might otherwise go to a landfill can serve as the source of biomass power?