A company has an on-premise Exchange Server 2010 SP1 environment. Client computers are joined to an Active Directory Domain Services (AD DS) domain. Some users are hosted in a cloud-based Exchange Server 2010 SP1 environment. An organization relationship exists between the on-premise and cloud-based environments. Administrative assistants with mailboxes in the on-premise environment must be able to view contacts in cloud-based user mailboxes.
You need to recommend a solution that meets the requirement.

What should you recommend?

A.
a sharing policy

B.
a remote domain

C.
a federation trust

D.
an Outlook protection rule