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问题 选择题

将淀粉碘化钾混合溶液装在羊皮纸制成的袋中，将此袋下半部浸泡在盛有蒸馏水的烧杯里，过一段时间后取烧杯中液体进行实验，下列现象能证明羊皮袋一定有破损的是

A．加入碘水变蓝色

B．加入NaI溶液不变蓝色

C．加入AgNO3溶液产生黄色沉淀

D．加入溴水变蓝色

答案

A、D

羊皮纸是一种半透膜，淀粉胶粒无法透过半透膜，但I－、K＋能通过半透膜进入蒸馏水中．A中加碘水变蓝色，说明其中有淀粉，可证明羊皮纸袋有破损．D中加入Br2水变蓝色，是溴与KI反应，置换出了I2，I2使淀粉变蓝色，也能证明羊皮纸袋有破损．B、C不能证明羊皮纸袋有破损．

单项选择题

The traditional model for systems development was that an IT department used （1） which is a process-centered technique, and consulted users only when their input or approval was needed. Compared with traditional methods, many companies find that JAD allows （2） to participate effectively in the requirements modeling process. When properly used, JAD can result in a more accurate statement of system requirements, a beret understanding of common goals, and a per commitment to the success of the new system. RAD is a （3） technique that speeds up information systems development and produces a functioning information system. While the end product of JAD is a(an) （4）, the end product of RAD is the new information system. The RAD model consists of tour phases. During the （5）, users interact with systems analysts and develop models and prototypes that represent all system processes, outputs, and inputs.

（4）处填（）。

A．data flow diagram

B．entity relationship model

C．requirements model

D．object model
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单项选择题

10千伏外来电源通过变电站母线转供其他出线时，应考虑电源侧保护定值调整，（）重合闸停用、联络线开关进线保护及重合闸停用

A、被转供的10千伏线路

B、电源线路

C、联络线路

D、相关线路
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