Final answer:
The nurse should verify the patient's identity and confirm the blood transfusion order first to ensure patient safety.
Step-by-step explanation:
The nurse should take action A. Verify the patient's identity and confirm the blood transfusion order first. It is crucial to ensure the patient's safety and prevent any potential errors before administering a blood transfusion. Verifying the patient's identity helps prevent accidental transfusion of blood to the wrong patient.
Obtaining vital signs and baseline assessment (option B) is important but can be done after verifying the patient's identity and confirming the blood transfusion order.