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: Pathology
A 3 cm squamous cell carcinoma of the retrornolar trigone and invading the mandible and the medial pterygoid muscle is at what TNM stage: 
Select and explain. 
A. Stage I, B. Stage II, C. Stage III, D. Stage IV
D: Stage IV
Answer: D: Stage IV 
Explanation: None