Your network contains an Active Directory forest.
The forest contains two domains named contoso.com and fabrikam.com.
The functional level of the forest is Windows Server 2003.
You have a domain outside the forest named adatum.com.
You need to configure an access solution to meet the following requirements:

– Users in adatum.com must be able to access resources in contoso.com.
– Users in adatum.com must be prevented from accessing resources in fabrikam.com.
– Users in both contoso.com and fabrikam.com must be prevented from accessing resources in adatum.com.
What should you create?

A.
a one-way realm trust from contoso.com to adatum.com

B.
a one-way realm trust from adatum.com to contoso.com

C.
a one-way external trust from contoso.com to adatum.com

D.
a one-way external trust from adatum.com to contoso.com

Explanation:
domain names were changed, so understand the question well
You need to make trust relationship where domain contoso.com trusts adatum.com.
http://technet.microsoft.com/en-us/library/cc728024(v=ws.10).aspx