The organisms A and B occur on the forest floor. They convert the dead parts of forest plants and dead parts of forest plants and dead bodies of forest animal into simple susbtances such as C,D and E which can be re-used by organisms F for their growth and development.
What is D ?

Answer

To solve the question, we need to identify what D is in the context of the organisms A and B that convert dead organic matter into simpler substances.

### Step-by-Step Solution:

1. **Identify Organisms A and B**: The question states that organisms A and B occur on the forest floor and convert dead parts of forest plants and animals into simpler substances. These organisms are likely decomposers, which play a crucial role in breaking down organic matter.

**Hint**: Think about what types of organisms are responsible for breaking down dead matter in ecosystems.

2. **Understanding the Process**: Decomposers, such as fungi and bacteria, break down dead organic material into simpler substances. This process is essential for recycling nutrients in the ecosystem.

**Hint**: Consider what happens to dead plants and animals in a forest. What do they turn into?

3. **Identify the Simple Substances**: The simpler substances produced by decomposers can include nutrients, carbon dioxide, and minerals. These substances are essential for the growth of other organisms in the ecosystem.

**Hint**: What are the basic components that plants need to grow? Think about gases and nutrients.

4. **Determine D**: In the context of the question, D refers to one of the simpler substances produced by the decomposition process. Since carbon dioxide is a gas that plants use for photosynthesis, it fits the description of a simple substance that can be reused by organisms (like plants).

**Hint**: Remember that plants take in carbon dioxide from the atmosphere for photosynthesis. What is the role of carbon dioxide in plant growth?

5. **Conclusion**: Based on the above reasoning, D is identified as carbon dioxide.

### Final Answer:
D is carbon dioxide.