Contoso Ltd, has an on-premises SharePoint environment. The Company plans to deploy SharePoint
Online.
You must use Active Directory Federation Service (AD FS). The global administrator account must be
able to access the Office 365 tenant even if AD FS is unavailable.You need to set up the global administrator account.
What should you do?

A.
In the Office 365 admin center, create a user named sp_admin@contoso.onmicrosoftcom.

B.
In the Office 365 admin center, create a user named sp_admin@contoso.com.

C.
In Active Directory Domain Services Users and Computers, create a user named sp_admm@contoso.onmicrosoftcom.

D.
In Active Directory Domain Services Users and Computers, create a user named sp_admin@contoso.com.

Explanation:
A complete set up of ADFS federates the entire domain of contoso.com. Even if you create a global admin
user in Office 365 using the @contoso.com domain the domain is federated so I believe you will be redirected you to your ADFS login page.
If you create a global admin in Office 365 and configure the UPN to use the domain suffix of contoso.onmicrosoft.com you will not be sent to the ADFS log in page.