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问题 填空题

在如图所示的电路中，电源电压不变，R2=10Ω．S1闭合、S2断开时，电流表的示数为0.2A．两开关都闭合时，电流表的示数为0.5A，则电阻R1=______Ω．

答案

U1=R1×0.2A，

U1=U2=U=R1×0.2A，

I=I1+I2=

U1
R1
+
U2
R2

=

R1×0.2A
R1
+
R1×0.2A
10Ω
=0.5A，

解得R1=15Ω．

故答案为：15．

写作题

现在，全国启动了“文明餐桌行动”，号召全国人民 “文明用餐，节俭惜福”。请结合图片，联系实际，适当发挥，以“Save(节约) Food and Eat Healthily”为题，写一篇80-100词的英语短文。文章开头已给出，不计入总词数。

waste too much       eat up all the food       eat junk food      eat a balanced diet

Save Food And Eat Healthily

The government has called on the pepole to save food and eat healthily so that we can enjoy our happy life. We middle school students should do something for it.

To save food, we                                                                    

                                                                                    

                                                                                      

       
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单项选择题

学龄前儿童的三餐分配要合理，以______为宜。

A．三餐一点制
B．四餐一点制
C．三餐二点制
D．四餐二点制
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