根据下面的文字资料回答 68～72 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．

第68题：文中（ 1 ）处正确的答案是（ ）。

A．SMTP

B．ICMP

C．RARP

D．IGMP