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
According to Boyd's classification, when the pain continues but the patient can still walk with effort is: 
Select and explain. 
A. Grade 1, B. Grade 2, C. Grade 3, D. Grade 4
B: Grade 2
Answer: B: Grade 2 
Explanation: Boyd’s classification:

Grade I: pain disappears, if the patient continues to walk
Grade II: pain continues, but the patient can still walk with effort
Grade III: pain compels the patient to take rest.