Choice "B" is correct. A firewall is a system of user identification and authentication that prevents unauthorized users from gaining access to network resources. This name may also be applied to a network node used to improve network traffic and to set up a boundary that prevents traffic from one segment from crossing over to another. The most common use is to prevent Internet users from gaining access to an organization's private intranet.
Choice "d" is incorrect. A login ID is used to identify a user and a password authenticates that user. Encryption is used to protect data in transmission and in storage.
Choice "c" is incorrect. A network server is a type of resource protected by the firewall.
Choice "a" is incorrect. There is no such thing as a network force field.