Final answer:
The correct action when observing early decelerations during the second stage of labor is to continue to monitor the fetal heart rate. This pattern is typically normal and doesn't immediately warrant interventions such as supplemental oxygen or emergency cesarean section.
Step-by-step explanation:
During the second stage of labor, when a nurse observes early decelerations on the fetal heart rate monitor, the appropriate action to take would be D. Continue to monitor the fetal heart rate. Early decelerations are typically a normal physiological response during the peak of a contraction and represent fetal head compression. They tend to occur at the peak of a contraction and resolve quickly once the contraction ends, and usually do not indicate fetal distress. Therefore, interventions such as changing the client's position, administering oxygen, or preparing for an emergency cesarean section wouldn't be indicated unless the heart rate pattern changes to a more concerning type of deceleration, like late decelerations or variable decelerations, or other signs of fetal distress are present.