For an Experience Cloud site that uses Salesforce as the identity provider, the supported login experiences are the standard page types intended for authentication. Salesforce supports a Login Discovery page, which helps identify the user and route them appropriately, and an Embedded Login page, which allows the login experience to be embedded into a branded front-end. These are purpose-built for sign-in scenarios. By contrast, a generic Experience Builder content page or a Lightning Experience page is not the same thing as a supported login page type for the site's authentication flow. The important distinction in Salesforce documentation is between pages designed for site content and pages designed to participate directly in the authentication journey. This is why options A, C work together as the correct solution.