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问题 选择题

下列各组离子能大量共存的是(　　)

A．Fe2+、K+、H+、NO3-

B．Na+、K+、AlO2-、CO32-

C．Na+、AlO2-、Cl-、HCO3-

D．Fe3+、Na+、AlO2-、NO3-

答案

答案：B

选择题
如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R，导轨电阻可忽略不计；MN为放在ab和cd上的一导体杆，与ab垂直，其电阻也为R；整个装置处于匀强磁场中，磁感应强度的大小为B，磁场方向垂直于导轨所在平面（指向图中纸面内）；现对MN施力使它沿导轨方向以速度v（如图）做匀速运动；令U表示MN两端电压的大小，则（　　）

A．U=vBl，流过固定电阻R的感应电流由b到d

B．U=vBl，流过固定电阻R的感应电流由d到b

C．U=vBl，流过固定电阻R的感应电流由b到d

D．U=vBl，流过固定电阻R的感应电流由d到b
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改错题
改错题.
Every one year, thousands of people visit the
city Venice. It's very beautiful. There are not any
read there, so there are not any cars,
buses and taxis either. There are canals only.
All of them add to 178 and one of them
is quite big while rest are small.
People move up and down the canals with boats.
Venice is sink now. It is going down.
It was said that in 2040 Venice might be
under water. The sea calling Adriatic(亚得里亚海)will cover it.		1.______
2.______
3.______
4.______
5.______
6.______
7.______
8.______
9.______
10.______
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