Question

what should you add to your ecocolumn to create the decomposition layer? only sand mosquito fish dead or decaying leaves and plant matter water and soil

Explanation:

To create a decomposition layer in an ecocolumn, materials that decompose (like dead organic matter) are needed. Sand is for a different layer (e.g., filtration), mosquito fish are consumers, water and soil are base layers. Dead/decaying leaves and plant matter provide the organic material for decomposition by decomposers.

Answer:

C. dead or decaying leaves and plant matter