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问题 单项选择题

Alice向Bob发送数字签名的消息M，则不正确的说法是（）。

A．Alice可以保证Bob收到消息M

B．Alice不能否认发送过消息M

C．Bob不能编造或改变消息M

D．Bob可以验证消息M确实来源于Alice

答案

参考答案：A

解析：

[分析]： 本题考查数字签名的相关概念。

数字签名设计为发送者不可否认、接收者可以验证但不能编造或篡改。所以选项B、C和D都是正确的。选项A显然是错误的。

单项选择题

进行全口义齿修复，患者微笑时，上唇微笑线到平面的直线距离约为上中切牙的（）。

A.切1/3长

B.切2/3长

C.中1/3长

D.中2/3长

E.颈1/3长
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单项选择题

VRML is a (71) for 3D multimedia and shared virtual worlds on the WWW. In comparison to HTML, VRML adds the next level of interaction, structured graphics, and extra (72) (z and time) to the presentation of documents. The applications of VRML are (73) , ranging from simple business graphics to entertaining WWW page graphics, manufacturing, scientific, entertainment, and educational applications, and 3D shared virtual worlds and communities.
X3D is the name under which the development of VRML is continued. X3D is based on XML and is backwards (74) with VRML. Furthermore, it is componentized, profiled, and extensible, which makes it possible to use X3D in very different (75) , from high-end visualizations to lightweight applications.

A．broad

B．implicit

C．explicit

D．special
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