DRAG DROP
Your network contains two Active Directory forests named contoso.com and adatum.com. Each forest contains an Active Directory Rights Management Services (AD RMS) root cluster. All servers run Windows Server 2012 R2.
You need to ensure that the rights account certificates issued in adatum.com are accepted by the AD RMS root cluster in contoso.com.
What should you do in each forest? To answer, drag the appropriate actions to the correct forests. Each action may be used once, more than once, or not at all. You may need to drag the split bar between panes or scroll to view content.
Answer: 
Explanation:
A trusted user domain, often referred as a TUD, is a trust between AD RMS clusters that instructs a licensing server to accept rights account certificates (the certificates identifying users) from another AD RMS server in a different Active Directory forest. An AD RMS trust is not the same as an Active Directory trust, but it is similar in that it refers to the ability of one environment to accept identities from another environment as valid subjects.
Illustration:
Reference: Trusted User Domain