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: Medicine
[{'content': 'A previously healthy 65-year-old woman is brought to the emergency department because of acute stroke. Examination shows acute bilateral lower extremity deep vein thrombosis. Injection of agitated saline contrast during echocardiogram shows the presence of bubbles crossing into the left atrium. \n\nThe presence of which of the following is most likely to explain her symptoms? \nSelect and explain. \nA. Biscupid aortic valve, B. Patent foramen ovale, C. Tetra logy of Fallot, D. Transposition of the great vessels', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]