Your network contains three Active Directory forests. Each forest contains an Active Directory Rights
Management Services (AD RMS) root cluster.
All of the users in all of the forests must be able to access protected content from any of the forests.
You need to identify the minimum number of AD RMS trusts required.
How many trusts should you identify?

A.
2

B.
3

C.
4

D.
6

Explanation:
http://technet.microsoft.com/en-us/library/dd772648%28v=ws.10%29.aspx
AD RMS Multi-forest Considerations