Blood Blood Group

Which of the following conditions causes erythroblastosis fetalis?

1. Mother ${\mathrm{Rh}}^{+\mathrm{ve}}$ and fetus ${\mathrm{Rh}}^{-\mathrm{ve}}$

2. Mother ${\mathrm{Rh}}^{-\mathrm{ve}}$ and fetus ${\mathrm{Rh}}^{+\mathrm{ve}}$

3. Both mother and fetus ${\mathrm{Rh}}^{-\mathrm{ve}}$

4. Both mother and fetus ${\mathrm{Rh}}^{+\mathrm{ve}}$