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
Large painful ulcers seen in which grade of mucositis: 
Select and explain. 
A. Grade 1., B. Grade 2., C. Grade 3., D. Grade 4.
C: Grade 3.
Answer: C: Grade 3. 
Explanation: 4 grades

Grade 1:  whitish area Asymptomatic
Grade 2:  ulcers(Small)
Grade 3:  large (painful)
Grade 4: entire oral mucosa.