Which Event Occurs Before All the Others, Leading to the Delivery

Multiple Choice

Which event occurs before all the others, leading to the delivery of a human baby?

A) An increase in the ratio of estrogen to progesterone
B) Pressure of the fetal head on the cervix communicated to the hypothalamus
C) An increase in secretion of oxytocin by fetal and maternal posterior pituitaries
D) Dilation of the cervix
E) A positive feedback loop involving oxytocin and uterine contractions