A 43-year-old Caucasian woman, previously in good health, presents to the emergency department with headache, blurred vision, and dizziness. Symptoms started 3 days ago and progressively worsened. Past medical history: hypertension, hypothyroidism, prior cholecystectomy. No known drug allergies. Medications: HCTZ 25 mg daily, Diltiazem CD 120 mg daily, and Levothyroxine 88 mcg daily. She ran out of all medications 2 weeks ago. Vital signs were normal, except for blood pressure 210/114 in the right arm, 215/115 left arm, 220/100 right leg, and 215/112 left leg. Physical exam: Heart - no visible or palpable PMI; normal S1 and S2 without murmur, rub, or gallop. Pulmonary - few faint RLL crackles, which cleared upon coughing. Remainder of the physical exam, including neurologic exam, was unremarkable.
CBC and BMP were unremarkable except for K+ 2.3 mEq/L.
EKG - NSR with one PVC. Chest X-ray - clear lung fields; normal pulmonary vasculature. CT head - no evidence of intracranial pathology.
Renal artery sonogram - Unremarkable.
Patient was treated with IV Nitroprusside and IV KCl 40 mEq x 2 doses and was admitted for further treatment. Over the next 2 days, patient's blood pressures gradually normalized with medical therapy; potassium levels remained low despite treatment.

best screening test for suspected diagnosis?
a. Renal artery duplex ultrasound
b. Renal magnetic resonance angiography
c. Renal artery angiography
d. Renal artery computed tomography (CT) angiography