**Core Concept**
Residual bodies are cellular structures formed during the breakdown of lysosomes. They are essentially the remnants of lysosomes that have fused with phagosomes or autophagosomes, leading to the degradation and recycling of cellular components. This process is crucial for maintaining cellular homeostasis and recycling cellular waste.

**Why the Correct Answer is Right**
Residual bodies are formed when lysosomes fuse with phagosomes or autophagosomes, resulting in the degradation of cellular waste and debris. This process is mediated by various enzymes, including acid hydrolases, that break down proteins, lipids, and other cellular components. The breakdown products are then recycled by the cell, allowing for the maintenance of cellular homeostasis. Residual bodies are often found in cells that are involved in the uptake and degradation of cellular waste, such as macrophages and hepatocytes.

**Why Each Wrong Option is Incorrect**
* **Option A:** Residual bodies are not formed by the fusion of lysosomes with the endoplasmic reticulum, as this would not result in the degradation of cellular waste. Instead, the endoplasmic reticulum is involved in protein synthesis and lipid metabolism.
* **Option B:** Residual bodies are not formed by the breakdown of mitochondria, as this would not result in the formation of residual bodies. Mitochondrial breakdown is instead mediated by the process of mitophagy.
* **Option C:** Residual bodies are not formed by the fusion of lysosomes with the Golgi apparatus, as this would not result in the degradation of cellular waste. Instead, the Golgi apparatus is involved in protein modification and lipid metabolism.

**Clinical Pearl / High-Yield Fact**
Residual bodies are often found in cells that are involved in the uptake and degradation of cellular waste, such as macrophages and hepatocytes. This process is crucial for maintaining cellular homeostasis and preventing the accumulation of toxic waste products.

**Correct Answer: C.**