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
Back action clasp is a modification of: 
Select and explain. 
A. Ring clasp, B. Embrasure clasp, C. Onlay clasp, D. Hairpin clasp
A: Ring clasp
Answer: A: Ring clasp 
Explanation: Back-action clasp

It is a modification of the ring clasp.
Here the minor connector is connected to the end of the clasp arm and the occlusal rest is left unsupported.

Disadvantages:

Lack of support to the occlusal rest reduces its function.
It has both biological and mechanical unsound principles.