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: Ophthalmology
[{'content': 'An otherwise healthy person who wears contact lenses develops a small ulceration of eye. What is the cause – \nSelect and explain. \nA. Acanthamoeba, B. Cytomegalovirus, C. Toxocarna, D. Toxoplasma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]