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
Which of the following is seen on electron microscopy of medullary thyroid carcinoma specimens? 
Select and explain. 
A. 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
D: Presence of electron-dense granules in the cytoplasm
Answer: D: Presence of electron-dense granules in the cytoplasm 
Explanation: Medullary carcinoma on electron microscopy reveals variable numbers of membrane-bound electron-dense granules within cytoplasm of neoplastic cells.