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问题 单项选择题

设置临时高压给水系统的单层、多层民用建筑，屋顶的消防水箱应设置在（）。

A.保证最不利点消火栓静水压力不低于0.07MPa处

B.保证最不利点消火栓水枪充实水柱达10m处

C.建筑物的最高处

D.相邻较高建筑物上

答案

参考答案：C

选择题

从地面竖直上抛一个质量为m的小球,小球上升的最大高度为H,设上升过程中空气阻力f恒定.对于小球从抛出到上升至最高处的过程,下列说法正确的是(    )

A．小球的动能减少了mgH

B．小球的机械能减少了fH

C．小球的重力势能增加了mgH

D．小球的加速度大于重力加速度g
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单项选择题

In a public-key cryptosystem, (71) encrypted with the public key can only be deciphered with the private key from the same (72) . Conversely, (71) encrypted with the private key can be decrypted only with the public key. Users can make their public keys (73) available or place them at a key distribution center or others to access. However, the private key must be (74) safe. In public-key systems there’s no (75) to find a safe channel for communicating a shared secret key.

（71）是（）

A.binarytext

B.hypertext

C.plaintext

D.supertext
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