在分布式数据库系统中，一般不适合作为衡量查询代价依据的是____

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问题单项选择题

在分布式数据库系统中，一般不适合作为衡量查询代价依据的是______。

A．CPU代价

B．I/O代价

C．通信代价

D．存储代价

答案

参考答案：D

解析：在集中式数据库系统中，查询代价主要是由CPU代价和I/O代价来衡量的，在分布式数据库系统中，由于数据分布在多个不同的场地上，使得查询处理中还要考虑站点间传输数据的通信代价。另外，分布式数据库的缺点之一就是复杂的存取结构。因此本题答案为D。

完形填空

In a small village, there lived a potter(陶工) who had a donkey. Every day his donkey would carry soil from the ______ to his house. Since the field was quite far off, the potter would ______ under a tree midway, tying(拴) his donkey nearby.
One day, the potter ____ to take the rope with which he tied the donkey every day. When he reached the ____, he became worried and didn’t know what to do. At that time, a saint(圣人) ____ to be passing by. When the potter told the saint what his ____ was, he said, “Take the ____ to the place where you tie him every day. ____ to tie him using an imaginary rope. He won’t run away.” The potter did what the saint had said.
When he woke up, to his ___ and relief, he found the donkey standing in the ____ place. But to his frustration, when he prepared to leave for ____, the donkey did not move. ____, the potter saw the wise saint again and told him about the donkey’s ____ behavior. The saint said, “Go and pretend to untie the rope.” The potter ____ the saint’s advice.
Now the donkey was ready to leave for home. The potter thanked the wise saint and went home ____ his donkey.

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单项选择题

根据《信息技术设备用不间断电源通用技术条件》（GB/T14715-1993）规定，在线式不间断电源输出过压保护功能试验，产品在正常工作时，调节输出电压使之产生过压，过压点电压应小于标称输出电压的（），此时产品应自动关机或切换到电池供电。若在电池供电时产生过压，产品应自动关机。

A、110％

B、120％

C、130％

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