Right option is (c) Pregnancy
The explanation: Erythroblastosis foetalis is a condition that may happen to a woman when she is pregnant. When a woman with RH- blood type conceives a baby with RH+ blood type, the body perceives it as a threat and starts producing antibodies. This can cause the baby to die in the womb and so RH factor must be monitored especially if the woman is RH-. Certain medications and treatments can help reverse this condition.