Biogas is produced during anaerobic fermentation of ..................... material.

Explanation

**Step-by-Step Solution:**

1. **Understanding Biogas**: Biogas is primarily composed of methane, which is a gas produced during the breakdown of organic materials in the absence of oxygen. This process is known as anaerobic fermentation.

2. **Identifying the Process**: The term "anaerobic fermentation" refers to the decomposition of organic matter by microorganisms in an environment devoid of oxygen. This process is crucial for the production of biogas.

3. **Recognizing the Raw Material**: The raw materials that undergo anaerobic fermentation to produce biogas are typically organic materials. These can include agricultural waste, animal manure, food waste, and other biodegradable materials.

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