This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gallbladder, Subject name: Surgery
According to 8th AJCC TNM classification of carcinoma Gallbladder, minimum number of LN involved in N2? 
Select and explain. 
A. 3, B. 4, C. 5, D. 6
B: 4
Answer: B: 4 
Explanation: 8th AJCC (2017) TNM classification of Ca. gall bladder N1 - Metastasis to 1 - 3 regional nodes. N2 - Metastasis to 4 or more regional nodes. M1 - Distant metastasis.