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: Dental
Kim's classification type IV: 
Select and explain. 
A. Incomplete isthmus between two canals, B. Well defined complete isthmus between two canals, C. 3 or more canals with complete or incomplete isthmus, D. 3 or more canals without any visible connections
C: 3 or more canals with complete or incomplete isthmus
Answer: C: 3 or more canals with complete or incomplete isthmus 
Explanation: Kim et al Classification
Root Apex cross-section
Narrow ribbon-shaped connection that contains pulp or pulpally derived tissue : ISTHMUS
According to Kim et al classification; there are 5 types:

Type I : Incomplete isthmus between 2 canals.
Type II : Well defined, complete isthmus between 2 canals.
Type III : Very short but complete isthmus between 2 canals.
Type IV : 3 or more canals with the complete or incomplete isthmus.
Type V : 3 or more canals without any visible connection.