$1)$Modern computer systems can run multiple processes at the same time by sharing physical resources such as CPU and memory among processes. In such a system, not considering performance, user A can assume that the execution of his$/$her processes will not be affected by the execution of unrelated processes of user B because the operating system a$.$ removes all data and code of one process from memory when another process runs. b$.$ does not switch CPU from a process of user A to another user's process until A$\text{'}$s processes complete their execution. c$.$limits a process's access to memory that only stores its code and data. d$.$ allows a process access to all memory that stores non$-$operating system code but only when the access is read $2)$ An attacker is able to exploit abuffer overflow vulnerability in the code of an operating system to turn off file access checks. As a result of this change in the TCB$,$ any user can access any file in the system.The reason for this uncontrolled access to files on this system is that, prior to the exploitation of the operating system or TCB$,$ it did not meet the following requirement a$.$Complete mediation b$.$ Tamper$-$proof c$.$Correctness d$.$ All of them