问题
选择题
下列说法中，正确的是[ ]
A．二氧化硅溶于水显酸性
B．二氧化硅是酸性氧化物，它不溶于任何酸
C．水玻璃露置空气中发生反应：Na2SiO3+H2O+CO2=Na2CO3+H2SiO3↓，所以碳酸酸性比硅酸酸性强
D．高温时纯碱和石英发生反应：Na2CO3+SiO2===Na2SiO3+CO2↑，所以硅酸酸性比碳酸酸性强
答案
答案：C
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下列说法中，正确的是[ ]
A．二氧化硅溶于水显酸性
B．二氧化硅是酸性氧化物，它不溶于任何酸
C．水玻璃露置空气中发生反应：Na2SiO3+H2O+CO2=Na2CO3+H2SiO3↓，所以碳酸酸性比硅酸酸性强
D．高温时纯碱和石英发生反应：Na2CO3+SiO2===Na2SiO3+CO2↑，所以硅酸酸性比碳酸酸性强
答案：C
| 根据短文内容，完成下面表格。 | ||||||||||||
| Anne and Joseph are talking about an interesting question. Why do some people change their names? There can be many reasons. Hanna changed her name to Anne because she thought it would be easier for people to remember. On the other hand, Joseph is thinking about changing his name to an unusual name because he wants to be different. People have a lot of reasons for changing their names. Film stars, singers, sportsmen and some other famous people often change their names because they want names that are not ordinary, or that have special sound. They chose the "new name" for themselves instead of the name their parents gave them when they were born. Some people have another reason for changing their names. They have moved to a new country and want to use a name that is usual there. For example, Li Kaiming changed his name to Ken Lee when he moved to the United States. He uses the name Ken at his job and at school. But with his family and Chinese friends, he uses Li Kaiming. For some people, using different names makes life easier in their new country. In many countries, a woman changes her family name to her husband's after she gets married. But today, many women are keeping their own family name and not using their husband's. Sometimes, women use their own name in some situations (情况) and their husband's in other situations. And some use both their own name and their husband's.
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如图所示，某人乘雪橇从雪坡经A点滑至B点，接着沿水平路面滑至C点停止，人与雪橇的总质量为70kg，表中记录了沿坡滑下过程中的有关数据，请根据图表中的数据解决下列问题（g=10m/s2）：
| 位置 | A | B | C |
| 速度（m/s） | 2.0 | 12.0 | 0 |
| 时刻（s） | 0 | 4 | 10 |
（2）设人与雪橇在BC段所受阻力恒定，求阻力大小．
（3）人与雪橇从B到C的过程中，求阻力的平均功率．
