确定网络的层次结构及各层采用的协议是网络设计中（）阶段的主要任务。

听力原文：W: Tom must be in a bad mood today. He hasn't said half a dozen words all afternoon.M: Oh, really? That's not like the Tom we know.Q: What does the man imply?(15)A．Tom is usually talkative.B．Tom has a very bad temper.C．Tom has dozens of things to attend to.D．Torn is disliked by his colleagues.

A.
M:
B.
Q:
C.Tom
D.
B．Tom
E.
C．Tom
F.
D．Torn
G.

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从目前的应用需求来看，下面（）不是全球多媒体网络必须具备的特性。

A.异构性
B.安全性
C.移动性
D.交互性

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