The following questions are related to the topic of access control. answer each one of them. (15 pts., 5 pts. for each part) a. a system allows both positive and negative access rights to be specified. a user in this system can be a member of several groups, and members of a group can include users as well as other groups (when group g1 is a member of group g2, it is called its subgroup). positive or negative access rights can be specified for a user or group. assuming negative rights take precedence over positive ones, how should the system decide if a certain user request should be granted based on its acl and the groups the user belongs to at the time the request is made? b. how should acls be implemented in such a system to improve efficiency? c. in unix, access check is performed when a file is opened. assume a design that separates the file activation (e. g., the open() call) from access check. a read call must check if the process? s uid/gid has read access and similar check should be done for writes. will this system have a time-to check-time-to-use (toctou) vulnerability? explain your answer.