刘伟家住在花园小区12栋，6单元4楼2号，他家的门牌号是[ ]

A．12-6-4-2

B．6-4-2-12

C．2-4-6-12

For each blank, choose the best answer from the four choices and write down on the answer sheet.
(71) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.
(72) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.
(73) functions with two layers of protocols. It can connect networks of different, speeds and can be adapted to an environment as it expands.

A. MAC address and IP address B. MAC address and port address
C. E-mail address and IP addressD. port number and IP address

A socket is composed of two addresses: (74) .Heterogeneous network environments consist of computer systems from (75) vendors that run different operating systems and communication protocols.