The correct option is C Parturition
Parturition is also called childbirth, is the process of bringing forth a child from the uterus, or womb. As the baby gradually leaves the uterus, the cavity of the uterus must become progressively smaller to permit the uterine wall to remain closely approximated to the baby. This maintains the expulsive force of the muscular contractions on the body of the baby. The mechanism for achieving this close approximation is through a slight shortening or retraction of the individual muscle fibers during each contraction. Slow delivery of the shoulders and body of the infant will permit the muscle fibers to retract and adjust to the reduction in size of the cavity, thereby promoting more efficient contractions.