The correct option is C myometrium
Oxytocin, a neurohypophysial hormone involved in numerous physiological processes, plays a central role in the mechanism of parturition and lactation.
Activation of oxytocin receptors causes myometrial contractions. Estrogen is the hormone that stimulates parturition by increasing the expression of genes associated with myometrial excitability, contraction and increases uterine sensitivity to oxytocin during the course of pregnancy.
The classical action of oxytocin is stimulation of the uterine smooth muscle contraction during labour. Before the onset of labor, uterine sensitivity to oxytocin markedly increases with strong upregulation of oxytocin receptors in the myometrium.
Uterine sensitivity to estrogen receptors is responsible for the vigorous contraction of parturition.