Final answer:
A 28-year-old woman delivers a baby boy. In order to monitor complications, the nurse should be most alert to changes in blood pressure and pulse (Option B) as these can indicate serious and potentially life-threatening complications.
Step-by-step explanation:
The question pertains to the monitoring of complications postpartum, where the nurse should be most alert to changes in blood pressure and pulse.
These vital signs can indicate serious issues such as hemorrhage or infection, which are critical to identify and treat promptly.
While complaints of pain, ambivalent feelings about becoming a mother, and the number of previous deliveries are significant, they do not immediately point to life-threatening complications and therefore are not the highest priority for a nurse to monitor right after delivery.
Hence, the correct answer is Option B.