How many layers form the diffusion membrane ?

Explanation

To answer the question "How many layers form the diffusion membrane?", we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- The diffusion membrane is crucial for gas exchange in the lungs, specifically in the alveoli, which are the small air sacs where oxygen and carbon dioxide are exchanged.

2. **Identifying the Structure**:
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