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': "In a chronic smoker with mild haemoptysis. He also gave a history of hypertension and obesity. Lab data showed raised ACTH levels, which were not suppressed by dexamethasone. The cause for the Cushing's syndrome in the patient is - \nSelect and explain. \nA. MEN I, B. Pituitary adenoma, C. Adrenal cortical adenoma, D. Ectopic ACTH secreting tumor", 'role': 'user'}, {'content': "Answer: D \nExplanation: Remember this\nIn normal person\xa0 \xa0→\xa0 Low dose dexamethasone suppresses cortisol secretion.\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0\xa0\nIn Cushing's syndromes\xa0\xa0→\xa0Low dose dexamethasone is unable to suppress cortisol secretion.\nWhen Cushing's syndrome is\xa0caused due to ectopic ACTH\xa0production\xa0\xa0→\xa0 Even high dose dexamethasone is unable to suppress cortisol secretion.", 'role': 'assistant'}]