Name the double walled sac, which cover the lungs in mammals.

Explanation

To answer the question, "Name the double-walled sac, which covers the lungs in mammals," we can follow these steps:

### Step 1: Understand the Question
The question is asking for the name of a specific structure in the respiratory system of mammals that has a double-walled configuration and serves to cover the lungs.

**Hint:** Focus on the anatomical structures associated with the lungs in mammals.

### Step 2: Identify the Structure
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