Why Is There Potential for a Woman's Body to Recognize

Why is there potential for a woman's body to recognize her fetus as foreign?

A) The fetus and mother are not genetically identical.
B) The mother may have an autoimmune disease and recognize self antigens as foreign.
C) The mother's immune system may be suppressed.
D) The fetus is separated from the mother's blood and immune system.
E) By the time the mother produces antibodies, the baby has been born.