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': 'Corneal dystrophies are: \nSelect and explain. \nA. Primary and unilateral, B. Primary and bilateral, C. Primary, bilateral, with systemic disease, D. Primary unilateral without systemic disease', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Corneal dystrophies are primary, bilateral and inherited disorder manifesting occasionally at bih but more usually during first or second decade and sometimes even later in life. Corneal dystrophies are of 3 types: anterior dystrophy, stromal dystrophy and posterior dystrophy.', 'role': 'assistant'}]