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.
70（）
A．HTTP
B．URL
C．HTML
D．TAG
