You are answering a USMLE-style medical question. Question: A 39-year-old man presents to the emergency department complaining of a sharp pain that radiates along his right hemithorax, which worsens with deep inspiration. He says this started abruptly about 6 hours ago. He says that he has not noticed that anything that makes his pain better or worse. He also denies any other symptoms. He works as a long-haul truck driver, and he informs you that he recently returned to the east coast from a trip to Utah. His medical history is significant for gout, hypertension, hypercholesterolemia, diabetes mellitus type 2, and acute lymphoblastic leukemia from when he was a child. He currently smokes 2 packs of cigarettes/day, drinks a 6-pack of beer/day, and he denies any illicit drug use. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 98/min, and respiratory rate 23/min. His physical examination shows minimal bibasilar rales, but otherwise clear lungs on auscultation, normal heart sounds, and a benign abdominal physical examination. Which of the following is the most reasonable 1st step towards ruling out the diagnosis of pulmonary embolism in a low-risk patient? Options: A) ECG B) V/Q scan C) D-dimer D) CT pulmonary angiogram with IV contrast Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.