单选题 Network frewalls are security devices used to stop or mitigate (    ) access to private networks connected to the Internet, especially intranets. The only trafle alowed on thev network is defined via firewall (     )-any other taff attempting to access the network is blockeD. Network firewalls sit at the (     ) line of a network, acting as a communicationsliaison between intemal and gxtemal devics, When properly configured, a firewall alws users to access any of the resources they need while simultaneously keeping out unwanted accesses. In addition to limiting access to a protected computer and network, a firewall can (     ) all traffit coming into or leaving a network, and manage remote access to a private network through secure authentication grtificates and logins. (回答此处 ) firewalls examine every packet that passes through the network and then accep or deny it as defined by rules set by the user.