Which Best Describes the Role of a Proxy Server

Which best describes the role of a proxy server?

A) A device that inspects Layer 2 - Layer 4 traffic running through it and denies or permits based on a set of policies.
B) An intermediary program, which acts as both a server and a client for the purpose of making requests on behalf of other clients.
C) An intermediary program that protects the resources of a private network from users on other networks.
D) A device that extracts the destination address of a packet, selects ten best path for the packet and forwards the packet the next device in the path.