Person with "O" blood group is called universal donor. Why?

Explanation

### Step-by-Step Solution:

1. **Understanding Blood Groups**: Blood groups are classified based on the presence or absence of specific antigens on the surface of red blood cells (RBCs). The main blood group system is the ABO system, which includes four blood types: A, B, AB, and O.

2. **Antigens and Antibodies**:
- **Type A**: Has A antigens on RBCs and B antibodies in plasma.
- **Type B**: Has B antigens on RBCs and A antibodies in plasma.
- **Type AB**: Has both A and B antigens on RBCs and no antibodies in plasma.
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