Reference:
https://docs.microsoft.com/en-us/powershell/module/exchange/new-activesyncdeviceaccessrule?view=exchange-ps

Reference:
https://docs.microsoft.com/en-us/powershell/module/exchange/move-and-migration/get-moverequest?view=exchange-ps
https://docs.microsoft.com/en-us/powershell/module/exchange/move-and-migration/resume-moverequest?view=exchange-ps

Reference:
https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-for-secure-mail-flow-with-a-partner

References:
https://docs.microsoft.com/en-us/powershell/module/exchange/email-addresses-and-address-books/new-emailaddresspolicy?view=exchange-ps
https://docs.microsoft.com/en-us/Exchange/email-addresses-and-address-books/email-address-policies/email-address-policies?view=exchserver-2019

Note that the question says, "ensure that all the users in the tenant can receive email messages by using the
@fabrikam.com email domain". This means just the users with mailboxes hosted in Exchange Online and does not include the users with on-premises mailboxes.
F: the first step is to add the Fabrikam.com domain to Microsoft 365.
D: then you have to verify the domain (verify that you own the domain).
E: create a script that runs the Set-Mailbox cmdlet to add an @fabrikam.com email address to each mailbox.
If you also wanted users with on-premise mailboxes to receive @fabrikam.com emails, you would also need to perform the options given in answers B (modify the email address policy) and C (add an accepted domain).