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
A ledge is created on the lingual surface of the full
cast crown, to accommodate the lingual clasp arm. The greatest advantage is that it provides for: 
Select and explain. 
A. Appropriate contact, B. Appropriate undercut, C. Survey line, D. Guiding plane
D: Guiding plane
Answer: D: Guiding plane 
Explanation: None