题目内容：
根据下列题干，回答题：In the following essay．each blank has four choices．Choose the most suitable one fromthe four choices and write down in the answer sheet．
A socket 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（ 1 ）computers attached to the net- work．A socket（ 2 ）two addresses：（ 3 ）．Sockets provide a（ 4 ）communication channel between one or more systems．There are（ 5 ）sockets separately using TCP and UDP．
请选择（ 1 ）处最佳答案
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