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问题 选择题

钡和钠相似，也能形成含O22-离子的过氧化物，则下列叙述错误的是 [ ]

A．过氧化钡的化学式是Ba2O2

B．1mol过氧化钠或过氧化钡跟足量水反应都生成0．5mol氧气

C．过氧化钡是离子化合物

D．过氧化钠或过氧化钡都是强氧化剂

答案

答案：A

单项选择题

（），列为较大事故。

A、繁忙千线客运列车脱轨18辆以上并中断铁路行车48h以上

B、客运列车脱轨2辆以上18辆以下并中断繁忙干线铁路行车24h以上或者中断其他铁路行车48h以上

C、客运列车脱轨2辆以上18辆以下

D、客运列车脱轨2辆以上
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单项选择题 共用题干题

Many of the activities performed during the preliminary investigation are still being conducted in(1)，but in much greater depth than before.During this phase,the analyst must become fully aware of the(2)and must develop enough knowledge about the(3)and the existing systems to enable an effective solution to be proposed and implementeD. Besidesthe(4)for process and data of current system,the deliverable from this phase also includes the(5)for the proposed system.

空白（5）为（）

A.hardware and software specification

B.system performance specification

C.formal requirements definition

D.general problem statement
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