Final answer:
The correct answer is that when HR plugins are installed, the necessary HR roles are automatically included in the Admin role, allowing System Administrators to access all HR applications in ServiceNow.
Step-by-step explanation:
The question pertains to access permissions within the ServiceNow platform, specifically after the installation of HR (Human Resources) plugins or applications. The correct answer to why a System Administrator can initially access all HR applications even though the HR Service Delivery (HRSD) application is scoped is option 1: 'When the HR plugins are installed, the necessary HR roles are added to the Admin role.' In ServiceNow, the 'admin' role typically encompasses all access rights, allowing users with this role to access all tables, objects, and applications within the ServiceNow instance. This is by design to ensure that system administrators can set up and configure the system, including scoped applications such as HRSD. An HR Admin or a ServiceNow security user does not usually need to manually assign these privileges to a system administrator.