Q. A 56-year-old man comes to the emergency department because of chest pain. The pain started one hour ago and has not been relieved with nitroglycerin. The patient's medical history is significant for hypertension, diabetes, and chronic obstructive pulmonary disease. The patient smoked 30 cigarettes/day for the last 35 years. His family history is non-contributory. Vital signs are normal except for tachycardia. ECG shows ST-segment elevation in the lead I and aVF. Additionally, ST segment depression is noted in the lead III and aVF. Which of the following arteries is likely occluded in the above patient?