单项选择题

案例分析题

For each blank．choose the best answerfrom the four choices and write down on the answer sheet．
（1）is a protocol that a host uses toinform.a router when it joins or leaves an Internet muhicast group．
（2）is an error detection code that most data communication networks use．
（3）is an interior gateway protocol that uses a distance vector algorithm topropagate routing information．
（4）is a transfer mode in which all types of information ate organized intofixed form.cells onan asynchronous or non－periodic basis over a range of media．
（5）is an identifier of a web page．

文中（ 1 ）处正确的答案是（）。