The question emphasizes the importance of Separation of Concerns (SoC) and the Principle of Least Privilege (PoLP). For Person A, who is a database administrator, the appropriate role is 'roles/spanner.databaseAdmin' as it grants full control over databases. Person B, an analyst generating metric reports, only needs read access, hence 'roles/spanner.databaseReader' is suitable. Application C, responsible for automatic backups, requires the ability to create and manage backups but not necessarily full database administration rights, making 'roles/spanner.backupWriter' the correct choice. Option A correctly assigns these roles, adhering to SoC and PoLP by providing each entity only the permissions necessary for their role.