题目内容：
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
参考答案：