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

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

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

Explanation:
http://technet.microsoft.com/en-us/library/dd772648(v=ws.10).aspx