单项选择题

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 an error detection code that most data communication networks use.

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