Which Feature Ensures That in the Human Placenta, Oxygen Will

Which feature ensures that in the human placenta, oxygen will be transferred from the mother's blood to the developing fetus's blood?

A) There are pseudogenes in the globin gene family.
B) The fetal form of hemoglobin binds oxygen more tightly than the adult form.
C) The fetal form of hemoglobin binds oxygen less tightly than the adult form.
D) The fetus has myoglobin in addition to hemoglobin.
E) The fetus lacks myoglobin.