Final answer:
The primary oocyte matures into a secondary oocyte, which can become a mature egg and three polar bodies, with one mature egg forming if fertilization occurs.
Step-by-step explanation:
The primary oocyte will mature into a secondary oocyte that has the potential to become a zygote if fertilized by a sperm. During the process of oogenesis, the primary oocyte completes the first meiotic division to produce the secondary oocyte and a smaller cell known as a polar body, which typically degenerates. If the secondary oocyte is not fertilized, it disintegrates; if it is fertilized, it completes meiosis II, producing a mature egg and another polar body. Therefore, the correct answer to the student's question is D. egg and three polar bodies.