What is the likely cause of the issue?

Universal containers (UC) has implemented ansp-Initiated SAML flow between an external IDP and salesforce. A user at UC is attempting to login to salesforce1 for the first time and is being prompted for salesforce credentials instead of being shown the IDP login page .

What is the likely cause of the issue?
A . The "Redirect to Identity Provider" option has been selected in the my domain configuration.
B . The user has not configured the salesforce1 mobile app to use my domain for login
C . The "Redirect to identity provider" option has not been selected the SAML configuration.
D . The user has not been granted the "Enable single Sign-on" permission

Answer: B