D. Transport of oxygen through a placenta to a fetus.
Explanation:
Zygotes are fertilized egg cell, zygotes aren't produced in the ovaries but ovums or egg cells are produced in the ovaries. So option A is false.
Fertilization is internal not external in human. Option B is wrong.
Production of milk happens in the mammary gland (the breast) not in the reproductive system. Option C is false.
Transport of oxygen through a placenta to a fetus. The placenta is a vascular organ which is implanted in the wall of the uterus (a part of the female reproductive system) and links to the foetus through the umbilical cord.
