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)hypefiinks,　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?

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)hypefiinks,　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?

(79)

(78)

在关系模型中，关系的“元数”(arlty)是指(21)。有关系只和S，R　∩　S的运算等价于(22)。设关系R和S的属性个数分别为r和5，则(R×S)操作结果的属性个数为(23)。

(76)

(75)

计算机中存放当前指令地址的寄存器称为(14)，在顺序执行程序时，当指令长度为32位，存储器按字节编址，每执行一条指令该寄存器自动加(15)。在数据传输过程中经常增加一位来检验传送的正确性，该位称为(16)位。

(73)

(72)

某计算机字长为8位，它用补码、原码或反码来表示带符号的二进制整数(最高一位为符号位)，则机器代码11111111所表示的十进制真值分别为(6)、(7)或(8)。