(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