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
Most common cause of solitary thyroid nodule is: 
Select and explain. 
A. Physiological goiter, B. Follicular adenoma, C. Colloid degenerations, D. Cysts
C: Colloid degenerations
Answer: C: Colloid degenerations 
Explanation: None