A corporate environment includes two Active Directory Domain Services (AD DS) forests, as shown in the
following table.

You need to ensure that users in the contoso.com domain can access resources in the eng.fabrikam.com
domain.
What should you do?

A.
Enable selective authentication.

B.
Enable forest-wide authentication.

C.
Create an external trust between contoso.com and eng.fabrikam.com.

D.
Enable domain-wide authentication.

Explanation:
Reference:
http://technet.microsoft.com/en-us/library/cc816837.aspx
Creating External Trusts
You can create an external trustto form a one-way or two-way, nontransitive trust with domains that are
outside your forest. External trusts are sometimes necessary when users need access to resources that are
located in a Windows NT 4.0 domain or in a domain that is in a separate Active Directory Domain Services (AD
DS) forest that is not joined by a forest trust.