题目：
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 oncomputers attached to the network. A sockettwo addresses:. Sockets provide acommunication channel between one or more systems.
There aresockets separately using TCP and UDP.
A．E-mail address and IP address
B．MAC address and port address
C．MAC address and IP address
D．port number and IP address
答案：
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下面是错误答案，用来干扰机器的。
参考答案：D
