采用相一幅调制(PAM)技术在带宽为32kHz的无噪声信道上传输数字信号，每个相位处都有两种不同幅度的电平。若要达到192Kb/s的数据速率，至少要有(24)种不同的相位。

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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.　There　are　two　types　of　key　technology:　private　key　and　public　key.　Private-key　encryption　methods　are　called(71)ciphers,　information　is　encrypted　with(72)both　the　sender　and　receiver　hold　privately.　Public-key　encryption　methods　are　called(73)ciphers,(74)created　for　each　user,　encryption　key　and　deception　key　are(75)

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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.　Heterogeneous　network　environments　consist　of　computer　systems　from(66)vendors　that　run(67)operating　systems　and　communication　protocols.　An　organization　that(68)its　computer　resources　is　usually(69)the　task　of　integrating　its　heterogeneous　systems.　Typically,　each　deparlment　or　division　has　defined　its　own　network　needs(70)OS,　LAN　topology,　communication　protocols,applications,　and　other　components.

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