An extremely rare occurrence in humans is a multiple pregnancy with the embryos at different stages due to fertilization weeks apart. What mechanism normally prevents this from happening?
A. The embryo's secretion of FSH and LH maintains the corpus luteum, keeping estradiol and progesterone high until the placenta takes over secretion of these hormones.
B. The follicle's secretion of polar bodies maintains the fimbriae, keeping estradiol and progesterone high until the fallopian tube takes over secretion of these hormones.
C. The embryo's secretion of GnRH maintains the corpus luteum, keeping FSH and LH high until the placenta takes over secretion of these hormones.
D. The embryo's secretion of hCG maintains the corpus luteum, keeping estradiol and progesterone high until the placenta takes over secretion of these hormones.
Answer: D
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