_______epithelium is composed of a single layer of cells and functions as a lining for body cavities, ducts and tubes.

Answer

To answer the question, we need to identify the type of epithelium that is composed of a single layer of cells and serves as a lining for body cavities, ducts, and tubes.

### Step-by-Step Solution:

1. **Understanding Epithelium Types**:
- Epithelium is classified into two main types: simple epithelium and compound epithelium.

2. **Identifying Simple Epithelium**:
- Simple epithelium consists of a single layer of cells. This is crucial because the question specifies that we are looking for an epithelium made up of a single layer.

3. **Identifying Compound Epithelium**:
- Compound epithelium, on the other hand, is made up of multiple layers of cells. Since the question specifies a single layer, we can eliminate compound epithelium as an option.

4. **Functions of Simple Epithelium**:
- Simple epithelium has various functions, including lining body cavities, ducts, and tubes. This aligns perfectly with the requirements of the question.

5. **Conclusion**:
- Based on the above analysis, the answer to the question is "simple epithelium".

### Final Answer:
**Simple epithelium** is composed of a single layer of cells and functions as a lining for body cavities, ducts, and tubes.