Your network contains two Active Directory forests named contoso.com and nwtraders.com.
Active Directory Rights Management Services (AD RMS) is deployed in each forest.
You need to ensure that users from the nwtraders.com forest can access AD RMS protected
content in the contoso.com forest.
What should you do?

A.
Add a trusted user domain to the AD RMS cluster in the nwtraders.com domain.

B.
Create an external trust from nwtraders.com to contoso.com.

C.
Add a trusted user domain to the AD RMS cluster in the contoso.com domain.

D.
Create an external trust from contoso.com to nwtraders.com.

Explanation:
http://technet.microsoft.com/en-us/library/hh311036.aspx
Using AD RMS trust

It is not necessary to create trust or federation relationships between the Active Directory
forests of organizations to be able to share rights-protected information between separate
organizations. AD RMS provides two types of trust relationships that provide this kind of
rights-protected information exchange. A trusted user domain (TUD) allows the AD RMS root
cluster to process requests for client licensor certificates or use licenses from users whose
rights account certificates (RACs) were issued by a different AD RMS root cluster. You add a
trusted user domain by importing the server licensor certificate of the AD RMS cluster to
trust.