以太网物理地址的长度是______。

(79)

(78)

(77)

(76)

Multipurpose Internet Mail Extension (MIME) is a (71) document messaging standard in theInternet enviroment.With MIME，users can send (72) Email messages that include audio，video，graphices，and text to any other user of TC/IP network.Richtext information can also be (73) into messages.It defines the fonts，formats，and (74) features of a document sothe document can be easily (75) on many different types of systems.

(75)

(74)

电子邮件中的两个协议中，(62)协议是接收邮件的协议，(63)协议是发送邮件的协议。

(73)

(72)

(70)

在HFC网络中，需要一个名为Cable MODEM的设备，它不单纯是一个调制解调器，而是多种设备的组合，但不包括(57)；它采用的复用技术是(58)。

(71)