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
Internal attachments for a partial denture is used: 
Select and explain. 
A. When restoring a palatal cleft, B. When abutment tooth has dental canes, C. When there is difficult in getting clasp retention, D. When restoring Lost vertical dimension
C: When there is difficult in getting clasp retention
Answer: C: When there is difficult in getting clasp retention 
Explanation: None