有一个文件系统，采用三级索引的结构。文件控制块中设置10个直接索引地址，一级索引，二级索引、三级索引地址各一个。文件页的大小恰好与磁盘块大小相等，有512个字节。现有一个文件，它的文件控制块已在内存，现要访问该文件的第2678页，必须启动磁盘(25)。

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Software　design　is　a(71)process　.It　requires　a　certain(72)of　flair　on　the　part　of　the　designer.　Design　can　not　be　learned　from　a　book　.It　must　be　practiced　and　learnt　by　experience　and　study　of　existing　systems　.A　well(73)software　system　is　straightforward　to　implement　and　maintain　,easily(74)and　reliable　.Badly(73)software　systems　,although　they　may　work　are(75)to　be　expensive　to　maintain　,difficult　to　test　and　unreliable.

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(66)is a protocol that a host uses to inform. a router when it joins or leaves an Internet multicast group.

(67)is an error detection code that most data conlmunication networks use.

(68)is an interior gateway protocol that uses a distance vector algorithm to propagate routing information.

(69)is a transfer mode in which all types of information are organized into fixed form. cells on an asynchronous or nonperiodic basis over a range of media.

(70)is an identifier of a web page.