(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 propagaterouting information.
(69) is a transfer mode in which all types of information are organized into fixed form cells on all asynchronous or nonperiodic basis over a range of media.
(70) is an identifier of a web page.
（69）处填（）。
A．ISDN
B．x.25
C．Frame Relay
D．ATM