Basically, a (71) is a standalone process or a set of integrated processes that runs on a router or server to control the flow of (72) application traffic (73) through it. Typically, firewalls are (74) on the entry point to a public network such as the Internet. They could be considered traffic cops. The firewall’ s (75) is to ensure that all communication between an organization’s network and the Internet conform to the organization’s security policies.

74（）

A．placed

B．place

C．put

D．get