Erythroblastosis foetalis can occur if

• A
  Mother is $Rh^{-}$ve and foetus is $Rh^{+}$ve
• B
  Both mother and foetus are $Rh^{-}$ve
• C
  Mother is $Rh^{+}$ve and foetus is $Rh^{-}$ve
• D
  Both mother and foetus are $Rh^{+}$ve