The wall of alveoli consists of simple ................. squamous epithelium.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Structure of Alveoli**: The alveoli are tiny air sacs located in the lungs and are crucial for the process of gas exchange. They are surrounded by a network of capillaries that facilitate the transfer of oxygen and carbon dioxide.

2. **Identifying the Type of Epithelium**: The wall of the alveoli is made up of epithelial tissue. Epithelial tissues are classified based on the number of cell layers and the shape of the cells.

3. **Determining the Characteristics of the Epithelium**:
- The term "simple" indicates that the epithelium consists of a single layer of cells. This is important for efficient gas exchange, as a thinner barrier allows for quicker diffusion of gases.
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