This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
[{'content': 'A 60-year-old male hypeensive had a stroke 2 weeks prior to this sudden attack of dyspnea. The present ECG shows changes of S1 Q3 T3 and the V/Q pulmonary scan shows major areas of reduced perfusion. What is the probable diagnosis? \nSelect and explain. \nA. Pneumothorax, B. Congestive cardiac failure, C. Pulmonary thromboembolism, D. Psychogenic dysfunction', 'role': 'user'}, {'content': "Answer: C \nExplanation: Dyspnoea is the most common symptom of pulmonary embolism,and tachypnoea is the most common sign.ECG in pulmonary embolism shows sinus tachycardia ,and S1Q3T3 sign-an S wave in lead I,a Q wave in lead III,and an inveed T wave in lead III.V/Q scan can be done if there is no previous cardiopulmonary disease,& it shows major areas of reduced perfusion due to increased pulmonary vascular resistance & impaired gas exchange. Reference:Harrison's medicine-18th edition,page no:2170-2172;Davidson's medicine-22nd edition,page no:722.", 'role': 'assistant'}]