Rationale:A. Placing the newborn in a radiant warmer may be indicated for temperature instability, but it does not directly address the observed signs of respiratory distress, jitteriness, and lethargy.B. Initiating phototherapy is typically done for newborns with hyperbilirubinemia (jaundice), which is not indicated by the symptoms described.C. Obtaining blood glucose by heel stick is the priority action because the symptoms described could indicate hypoglycemia, especially in a newborn. Prompt assessment and management of blood glucose levels are essential.D. Measuring the newborn's blood pressure is not typically a priority in this situation unless there are specific indications, such as suspected cardiovascular abnormalities.