Passage Summary: Good compost helps plants grow, but if it smells like ammonia, it's not ready yet and you shouldn't use it.

Reasoning: The text provides criteria for good compost and specific warnings against using ammonia-smelling compost because it indicates incomplete decomposition.

Analysis: We need to find a statement that must be true based on these rules. We know that ammonia smell implies insufficient decomposition, and we know that if it hasn't decomposed enough, it shouldn't be used for soil drainage and fertility. Therefore, any compost that is appropriate for those uses must not have a strong ammonia smell. Look for an answer that connects the 'appropriateness for use' with the 'state of decomposition' or 'smell.'