For each blank，choose the best answer from the four choices and write down on the answer sheet．
(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 communication 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 non -periodic basis over a range of media.
(70) is an identifier of a web page.
A．SMTP
B．ICMP
C．RARP
D．IGMP