For each blank，choose the best answer from the four choices and write down on the answer sheet．
（） is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast group．
（） is an error detection code that most data communication networks use．
（） is an interior gateway protocol that uses a distance vector algorithm to propagate routing information．
（） 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.
（） is an identifier of a web page.

（） is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast group．