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: Surgery
The characteristic feature of medullary carcinoma: 
Select and explain. 
A. Non follicular histological appearance., B. Origin from parafollicular 'C' cells., C. Its secretion of calcitonin., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: None