Which terminology is being described below?

Which terminology is being described below?
These 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.

A.
Shortcut Trusts

B.
Realm Trusts

C.
Forest Trusts

D.
External Trust

Explanation:
You can create an external trust to form a one-way or two-way, nontransitive trust with domains
that are outside your forest
http://technet.microsoft.com/enus/library/cc775736%28v=ws.10%29.aspx Trust types

http://technet.microsoft.com/en-us/library/cc731297.aspx
Understanding When to Create a Realm Trust When to create a realm trust You can establish a realm
trust between any non-Windows Kerberos version 5 (V5) realm and an Active Directory domain. This
trust relationship allows cross-platform interoperability with security services that are based on
other versions of the Kerberos V5 protocol, for example, UNIX and MIT implementations. Realm
trusts can switch from non transitive to transitive and back. Realm trusts can also be either one-way
or two way.