The correct answer is the implementation of role-based access control (RBAC). RBAC is an administrative control that ensures employees are only granted access rights that are necessary to perform their jobs. In this scenario, RBAC would prevent managers from arbitrarily increasing their privileges, as their roles do not require such access, thereby enforcing separation of duties. While mandatory vacations could highlight if any inappropriate access or system dependencies exist, they do not prevent the escalation of privileges. Time-of-day restrictions also do not prevent the managers from granting themselves higher access during allowed hours. Implementing multifactor authentication would increase security but does not directly address the issue of inappropriate privilege escalation.