Final answer:
The 2nd stage of labor and delivery begins with the onset of contractions and ends with the delivery of the placenta.
Step-by-step explanation:
The second stage of labor and delivery begins with cervical dilation and ends with expulsion of the newborn or birth of the baby. During this stage, the cervix must dilate to approximately 10 cm to allow the baby to pass through into the birth canal. As the uterus contracts, the mother will use her abdominal muscles to help push and aid in the delivery of the newborn. Following the birth of the baby, stage three involves the passage of the placenta, which has now completely disengaged from the uterine wall.
Answering the initial question, the correct option is b) Onset of contractions, delivery, placenta. However, none of the provided options perfectly fits the stages outlined, as stage two specifically refers to full dilation and expulsion of the newborn, whereas the delivery of the placenta belongs to stage three.