已知文法G[A]，它定义的语言描述为(39)。　　　　G[A]：A→0B|1C　　　　　　　　　　B→1|1A|OBB　　　　　　　　　　C→O|OA|lCC

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A　Web　browser　is　simply　a　terminal　emulator,　designed　to　display　text　on　a　screen.　The　two　essential　differences　between　an　ordinary　terminal　emulator　and　a　Web　browser　are　that　the　browser　knows　how　to　deal　with(71),　and　that　it　has　a　mechanism　for(72)graphical　files.　Display　text,　display　graphics,　and(73)hyperlinks-there's　99　percent　of　the(74)value.　That's　not　to　say　that　the　manufacturers　didn't　go　all-out　to　attach　a　hyperactive　efflorescence　of　useless　capabilities　onto　their　browsers.　Remember　when　media　channels　in　the　browser　were　a　big　deal,　instead　of　the　clutter　you　can't　wait　to　delete　from　your　favorites　of　bookmarks　menu　?　Remember　when　client-side　Java　applets　were　supposed　to　become　the　preferred(75)for　application　development?　Remember　frames　and　all　their　nasty　side　effects?

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Most　computer　systems　are(66)to　two　different　groups　of　attacks:　Insider　attacks　and　outsider　attacks.　A　system　that　is　known　to　be(67)to　an　outsider　attack　by　preventing(68)from　outside　can　still　be　vulnerable　to　the　insider　attacks　accomplished　by　abusive　usage　of(69)users.　Detecting　such　abusive　usage　as　well　as　attacks　by　outsides　not　only　　provides　　information　on　damage　assessment,　but　also　helps　to　prevent　　future　attacks.　These　attacks　are　usually(70)by　tools　referred　to　as　Intrusion　Detection　Systems.