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 domaincan 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.