Final answer:
The roles that cannot be delegated usually include those with high-level permissions, such as 'role_administrator' and 'admin role_delegator', due to the security risks associated with improper delegation.
Step-by-step explanation:
In the context of user permissions and access control within an organizational structure or information system, certain roles are considered to have high-level privileges that should not be delegated. Looking at the options provided, role_administrator and admin role_delegator are typically associated with high-level permissions.
These roles are generally responsible for managing other user roles and permissions, and therefore, they have the authority to grant or revoke access rights. Consequently, it would not be appropriate to delegate these roles as it could pose a security risk to the system or organization. In contrast, roles such as just a 'user' or a normal 'role_delegator' might be regular user roles with lesser privileges which can be delegated more freely depending on organization policies.