Business Rule is server-side, so it uses GlideSystem API. gs.hasRoleExactly doesn't exist In a Business Rule, the following returns true if the currently logged in user has the admin role:
gs.hasRole('admin'). This is the correct answer because gs is the GlideSystem object, which provides methods for performing system operations, and hasRole is a method that checks if the current user has the specified role. For example, gs.hasRole('admin') will return true if the current user has the admin role, and false otherwise.
The following do not return true if the currently logged in user has the admin role in a Business Rule:
g_form.hasRoleExactly('admin'). This is not correct because g_form is the GlideForm object, which provides methods for manipulating forms, and hasRoleExactly is a method that checks if the current user has exactly the specified role and no other roles. For example, g_form.hasRoleExactly('admin') will return true if the current user has only the admin role, and false if the current user has the admin role and any other role.
g_form.hasRole('admin'). This is not correct because g_form is the GlideForm object, which provides methods for manipulating forms, and hasRole is a method that checks if the current user has the specified role or any role that contains the specified role. For example, g_form.hasRole('admin') will return true if the current user has the admin role or any role that contains the admin role, such as admin_ui or admin_script.
gs.hasRoleExactly('admin'). This is not correct because gs is the GlideSystem object, which provides methods for performing system operations, and hasRoleExactly is not a valid method of the gs object. There is no method that checks if the current user has exactly the specified role and no other roles in the gs object. Reference: Business Rules, GlideSystem, GlideForm

In ServiceNow, the Event Registry is a table that contains a record for every event recognized by the system. It allows ServiceNow to respond when these events are generated. By registering events, the system can automate activities such as triggering notifications or executing script actions when specific events occur. Therefore, the correct answer is A.
The other options are not accurate descriptions of the Event Registry:
B . The Event Log which lists all Events that have been generated: This describes the Event Log, not the Event Registry.
C . A Workflow which is launched every time an Event is generated; used to debug Events: This is not how the Event Registry functions.
D . The method used in server-side scripts to generate Events and pass parameters: This describes the gs.eventQueue() method, not the Event Registry.
For more detailed information, refer to the official ServiceNow documentation on the Event Registry.