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: ENT
A patient has carcinoma of right tongue on its lateral border of anterior 2/3rd, with lymph node of size 4 cm in level 3 on left side of the neck, stage of disease is: 
Select and explain. 
A. NO, B. N1, C. N2, D. N3
C: N2
Answer: C: N2 
Explanation: Classification of stage of tumor of oral cavity based on size of lymph node.