This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid Tumor, Subject name: Pathology
[{'content': 'Which of the following is seen on electron microscopy of medullary thyroid carcinoma specimens? \nSelect and explain. \nA. Presence of electron-dense granules in the nucleus, B. Presence of electron-dense granules in the mitochondria, C. Presence of electron-dense granules in the endoplasmic reticulum, D. Presence of electron-dense granules in the cytoplasm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Medullary carcinoma on electron microscopy reveals variable numbers of membrane-bound electron-dense granules within cytoplasm of neoplastic cells.', 'role': 'assistant'}]