Early computer networks used leased telephone company lines for their connections. The U.S. Defense Department was concerned about the inherent risk of this single-channel method for connecting computers, and its researchers developed a different method of sending information through (71) channels. In 1969, Defense Department researchers in the Advanced Research Projects Agency (ARPA) used this network model to connect four computers into a network called the ARPANET. The ARPANET was the earliest of the(72)that eventually combined tobecome what we now call the Internet.
The Internet provides only the physical and logical infrastructure that (73) millions of computers together. Many believe that the World Wide Web (WWW, or simply the Web) provides the killer application (制胜法宝）for this global network. The Web is considered the content of the (74)，providing all sorts of information by using a rich set of tools that manage and link text, graphics,, sound, and video. Providing and viewing information on the Web is accomplished using server applications and client applications.
If you’ve already explored the Web, you’ll recognize the client-side application as the Web browser. A Web browser receives, interprets, and displays(75)of information from the Web.
The user can navigate within pages, jump to other pages by clicking hypertext links, and point to just about any page on the Web.
