Erythroblastosis foctalis is casued when:

Options

A. `Rh^(-)` female & `Rh^(+)` male
B. `Rh^(+)` female & `Rh^(-)` male
C. `Rh^(+)` female & `Rh^(+)` male
D. `Rh^(-)` female & `Rh^(-)` male

Answer

### Step-by-Step Solution:

1. **Understanding Erythroblastosis Fetalis**:
Erythroblastosis fetalis is a hemolytic disease that occurs in a fetus or newborn when there is an incompatibility between the blood types of the mother and the fetus, particularly involving the Rh factor.

2. **Identifying the Blood Types**:
The Rh factor can be either positive (Rh+) or negative (Rh-). An Rh+ individual has the D antigen on the surface of their red blood cells, while an Rh- individual does not.

3. **Analyzing the Options**:
- **Option A**: Rh positive male and Rh negative female
- **Option B**: Rh positive female and Rh negative male
- **Option C**: Rh positive female and Rh positive male
- **Option D**: Rh negative female and Rh negative male

4. **Determining the Correct Pairing**:
- When an Rh- female conceives a child with an Rh+ male, the child can inherit the Rh+ factor. This can lead to the mother’s immune system recognizing the Rh+ blood cells of the fetus as foreign and producing antibodies against them.
- In subsequent pregnancies, if the mother has developed these antibodies, they can cross the placenta and attack the red blood cells of another Rh+ fetus, leading to erythroblastosis fetalis.

5. **Conclusion**:
The correct answer to the question is **Option A: Rh positive male and Rh negative female**. This pairing can lead to the development of erythroblastosis fetalis in the fetus.