Contoso, Ltd, has an Office 365 tenant. You configure Office 365 to use the domain contoso.com, and you verify the domain. You deploy and configure Active Directory Federation Services (AD FS) and Azure Active
Directory Connect with password synchronization. You connect to Azure Active Directory by using a Remote
Windows PowerShell session.
You need to switch from using AD FS to using password-synced passwords on the Office 365 verified domain.
Which Windows PowerShell command should you run? can use the Entire namespace conversion approach. To convert the desired namespace from Federated to single-sign-on-to-password-sync.aspx

A.
Convert-MsolDomainToFederated -DomainName contoso.com

B.
Convert-MsolDomainToStandard -DomainName contoso.com

C.
Convert-MsolFederatedUser

D.
Set-MsolDomainAuthentication -DomainName contoso.com

Explanation:

To switch large sets of users from federated authentication to managed authentication with password sync you
Managed, you have to use the Convert-MsolDomainToStandard cmdlet.
References: https://social.technet.microsoft.com/wiki/contents/articles/17857.dirsync-how-to-switch-from-