What equipment should you use if you want to route calls between a branch in a private network and a branch in a public network, hiding the networks between them?

What equipment should you use if you want to route calls between a branch in a private network
and a branch in a public network, hiding the networks between them?

A.
Cisco Unified Border Element

B.
MGCP gateway

C.
H.323 gateway

D.
Cisco Unified Communications Manager