Exam AZ-300 topic 4 question 23 discussion

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Your network contains an Active Directory forest named fabrikam.com. The forest contains two child domains named corp.fabrikam.com and research.fabrikam.com.
You have an Azure subscription that contains an Azure Active Directory (Azure AD) tenant named contoso.com.
You install Azure AD Connect and sync all the on-premises user accounts to the Azure AD tenant. You implement seamless single sign-on (SSO).
You plan to change the source of authority for all the user accounts in research.fabrikam.com to Azure AD.
You need to prevent research.fabrikam.com from resyncing to Azure AD.
Solution: You use Active Directory Domains and Trusts from a computer joined to fabrikam.com.
Does this meet the goal?

Suggested Answer: B 🗳️
Instead you should customize the default synchronization rule.
Note:
To delete a custom domain name, you must first ensure that no resources in your directory rely on the domain name. You can't delete a domain name from your directory if:
✑ Any user has a user name, email address, or proxy address that includes the domain name.
✑ Any group has an email address or proxy address that includes the domain name.
Any application in your Azure AD has an app ID URI that includes the domain name.

References:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-create-custom-sync-rule