This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Investigation of choice for pulmonary embolism \nSelect and explain. \nA. CT scan, B. Contrast CT, C. Ventillation - Perfusion Scan, D. MRI', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Contrast CT', 'role': 'assistant'}]