Name the body structure concerned with the given functional activity :
Combines with the oxygen in the lungs.

Explanation

**Step-by-Step Solution:**

1. **Identify the Functional Activity**: The question asks for the body structure that combines with oxygen in the lungs.

2. **Understand the Role of Hemoglobin**: Hemoglobin is a protein found in red blood cells. Its primary function is to transport oxygen from the lungs to the rest of the body.

3. **Process of Oxygen Binding**: In the lungs, hemoglobin binds with oxygen molecules. This process occurs when blood passes through the capillaries in the lungs, where oxygen concentration is high.

...