This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
A 67-year-old hypertensive man presents with lower abdominal pain and back pain. An expansive abdominal mass is palpated lateral and superior to the umbilicus. What is the best investigation for this patient? 
Select and explain. 
A. X-ray KUB, B. Ultrasound abdomen, C. Coronary angiography, D. Intravenous Pyelography
B: Ultrasound abdomen
Answer: B: Ultrasound abdomen 
Explanation: Ans. B Ultrasound abdomenRef: CMDT 2019 pg. 492The presentation is suggestive of abdominal aortic aneurysm. The size should be evaluated by ultrasound and surgical repair is advisable if the aneurysm is greater than 5.5 cm in diameter as it can exhibit spontaneous rupture.