Which statement about the function of a gatekeeper is true?

A.	A gatekeeper improves call routing between servers within a single Cisco Unified Communications Manager cluster.
B.	A gatekeeper can replace the dial plan of a Cisco Unified Communications Manager cluster.
C.	A gatekeeper can simplify the dial plan between many different Cisco Unified Communications Manager clusters.
D.	Gatekeepers can be implemented to deploy RSVP-based CAC.