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
In root end preparation: 
Select and explain. 
A. Tunnel type cavity is prepared, B. Class I cavity is prepared, C. Vertical slot is prepared, D. Any of the above
B: Class I cavity is prepared
Answer: B: Class I cavity is prepared 
Explanation: Car and Bentkover defined an ideal root-end preparation as "A class I preparation at least 3.0 mm into root dentine with walls parallel to a coincident with the anatomic outline of the pulp space".
Five requirements suggested for a root end preparation to fulfill:

The apical 3 mm of root canal must be freshly cleaned and shaped.
Preparation must be parallel to the anatomic outline of the pulp cavity.
Creation of an adequate retention form.
Removal of all isthmus tissue if present.
Remaining dentin walls should not be weakened.

Textbook of Endodontics Nisha Garg 3rd Ed