This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
[{'content': 'Most common cause of ptosis - \nSelect and explain. \nA. Myasthenia gravis, B. Paralysis of 3rd nerve, C. Idiopathic, D. Congenital', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Congenital weakness of the levator palpebrae superioris innervated by third cranial nerve III occulomotor . Ref: Ak khurana 6th edition page no:378', 'role': 'assistant'}]