Consider a system which uses a ring-based access control mechanism with 9 rings (from 0 to 8). Consider two procedures running in this system p1 and p2. Procedure p1 is executing and needs to invoke procedure p2. Procedure p2’s bracket is (3,5,6). Procedure p2’s ACL gives p1 full (read, write, append, and execute) rights to p2. In which ring(s) must p1 execute for the following to happen? p1 can invoke p2, but a ring-crossing fault occurs p1 can invoke p2 provided that a valid gate is used as an entry point p1 cannot invoke p2 p1 can invoke p2 without any ring-crossing fault occurring, but not necessary through a valid gate.