For each blank，choose the best answer from the four choices and write down on the answer sheet．
(1) is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast 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 to propagate routing information．
(4) 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.
(5) is an identifier of a web page.
4（）
A．ADSL
B．ATM
C．Frame Relay
D．DDN
