The pigment present in red blood cells.

Explanation

### Step-by-Step Solution:

1. **Identify the Question**: The question asks for the pigment present in red blood cells (RBCs).

2. **Recall the Function of RBCs**: Red blood cells are primarily responsible for transporting oxygen from the lungs to the tissues and returning carbon dioxide from the tissues back to the lungs.

3. **Identify the Key Pigment**: The primary pigment in red blood cells that facilitates oxygen transport is hemoglobin.

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