Back action clasp is a modification of:: (A) Ring clasp, (B) Embrasure clasp, (C) Onlay clasp, (D) Hairpin clasp
Answer is A. 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.