单项选择题

案例分析题

In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.
A  （） is basically an end point of a communication link between two applications. Sockets that extend over a network connect two or more applications running on separate computers at tached to the network. A socket  （） two addresses:  （） . Sockets provide a  （） communication channel between one or more systems.
There are stream and datagram sockets separately using TCP and  （）.

Sockets provide a （） communication channel between one or more systems.

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