Movement into and out of cells — practice question

In the human gas exchange system, where can squamous epithelial cells be found?

• Atrachea ✓, bronchus ✓, alveolus ✓
• Btrachea ✓, bronchus \times, alveolus ✓
• Ctrachea \times, bronchus ✓, alveolus \times
• Dtrachea \times, bronchus \times, alveolus ✓