The primary purpose of NAT (Network Address Translation) is to:

A.
Translate IP (Internet Protocol) addresses into user friendly names.

B.
Hide internal hosts from the public network.

C.
Use on public IP (Internet Protocol) address on the internal network as a name server.

D.
Hide the public network from internal hosts.

Explanation:
NAT effectively hides your network from the world. This makes it much harder to determine what systems exist on the other side of the router.
Reference: Security + (SYBEX) page 29