Which statement about the function of a gatekeeper is true?

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.