How many major types of blood have scientists discovered?

Options

A. One: Type ''O''
B. Two: white cells and red cells
C. Three: white cells, red cells, and plasma
D. Four: Types A, B, AB, and O

Answer

**Step-by-Step Solution:**

1. **Understanding Blood Groups**: Scientists have classified human blood into different types based on the presence or absence of certain antigens on the surface of red blood cells.

2. **ABO Blood Group System**: The most widely recognized classification system is the ABO blood group system. This system categorizes blood into four major types.

3. **Identifying the Blood Types**: The four major blood types in the ABO system are:
- Type A
- Type B
- Type AB
- Type O

4. **Conclusion**: Therefore, scientists have discovered four major types of blood in the ABO blood group system.

5. **Final Answer**: The correct answer is that there are four major types of blood.

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