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问题 单项选择题

数据库管理系统有多项功能，其中进行数据的安全性检查和完整性检查的功能是______。

A．数据定义
B．数据操纵
C．数据运行管理
D．数据库维护

答案

参考答案：C

单项选择题

载荷前移，（）。

A．尾倾减小

B．首倾增大

C．平均吃水增大

D．A、B
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单项选择题

(66) is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed,length bit string. (67) is a protocol that most USENET machines now use it to allow news articles to propagate from one machine to another over a reliable connection. (68) is an approach preferred by cable TV providers. In this solution the fiber terminates at an opt~electrical converter and the final segment is a shared coaxial cable. (69) is a device used to connect two separate network that use different communication protocol. (70) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

A．ADSL

B．FTTC

C．HFC

D．FTTH
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