Name the sac which surrounds the lungs.

Explanation

**Step-by-Step Solution:**

1. **Identify the Structure Surrounding the Lungs**: The question asks for the name of the sac that surrounds the lungs.

2. **Recall the Name of the Sac**: The sac that surrounds the lungs is called the "pleura."

3. **Understand the Composition of the Pleura**: The pleura consists of two thin layers of tissue:
- **Parietal Pleura**: This is the outer layer that is attached to the chest wall.
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