You have just administered 0.4 mg of sublingual nitroglycerin to a 60-year-old woman with severe chest pain. The patient is receiving supplemental oxygen and has an IV line of normal saline in place. After 5 minutes, the patient states that the pain has not subsided. You should:

A. repeat the nitroglycerin.
B. give her a 250-mL saline bolus.
C. administer 2 to 4 mg of morphine. D. reassess her blood pressure.