Problem 3 (MULTICS): Consider Multics procedures p and q. Procedure p is executing and needs to invoke procedure q. Procedure qs access bracket is (5, 6) and its call bracket is (6, 9). Assume that qs access control list gives p full (read, write, append, and execute) rights to q. In which ring(s) must p execute for the following to happen? a. p can invoke q, but a ring-crossing fault occurs. b. p can invoke q provided that a valid gate is used as an entry point. c. p cannot invoke q. d. p can invoke q without any ring-crossing fault occurring, but not necessarily through a valid gate.