Occurs when the mother's body begins to fight off foreign blood protein produced by the fetus.
a. non-teratogenesis.
b. rh factor incompatibility.
c. reduced blood oxygenation.
d. a neural tube defect.

The correct answer is b. Rh factor incompatibility.

Explanation:

Rh factor incompatibility occurs when a mother's body makes antibodies against the Rh antigen present in fetus blood which can lead to fetal death if not treated.  

Commonly it occurs when an Rh⁻ woman carries a fetus which is Rh⁺. During first pregnancy complications are not serious because memory was not built against Rh⁺ antigen and only during the delivery mother's blood comes in contact with fetal blood.

But during second pregnancy memory was already present in the mother's body against Rh⁺ antigen because of the earlier exposure during first pregnancy, therefore, a quick and enhanced immune response is generated against the fetal blood antigen which results in erythroblastosis fetalis.

Therefore the right answer is b. Rh factor incompatibility.