Setting the IdentityProvider as default and enabling the Redirect to the Identity Provider setting on the SAML Configuration will automatically redirect users to the login page of the external Identity Provider when using an SP-Initiated SAML flow with Salesforce as a ServiceProvider1. Option A is incorrect because Visualforce is not a supported method for redirecting users to the Identity Provider login page2. Option B is incorrect because enabling the Redirect to the Identity Provider setting under Authentication Services on the My Domain Configuration will only redirect users to the Identity Provider login page when using an IdP-Initiated SAML flow3. Option C is incorrect because removingthe Login page from the list of Authentication Services onthe My Domain configuration will not affect the SP-Initiated SAML flow, and may cause other issues with authentication4.