You have a Microsoft 365 subscription linked to an Azure Active Directory (Azure AD) tenant named contoso.onmicrosoft.com.
In the subscription, an administrator adds two custom domains named sub1.contoso.onmicrosoft.com and sub2.contoso.onmicrosoft.com and the objects shown in the following table.

You plan to delete sub1.contoso.onmicrosoft.com and sub2.contoso.onmicrosoft.com.
Which objects must you delete or modify manually before you can delete the domains? To answer, select the appropriate options in the answer area.
NOTE: Each correct selection is worth one point.

Correct Answer:

Explanation

Anything with an email address in the subdomain needs to be removed or moved to another domain. This includes users, mail-enabled security groups, distribution groups and contacts. Office 365 groups will also need to be removed from the subdomains (they cannot be moved to another domain). However, the only Office 365 group in this question is in the parent domain, not the subdomains.
Reference:
https://docs.microsoft.com/en-us/microsoft-365/admin/get-help-with-domains/remove-a-domain?view=o365-wo