题干

Na2CO3俗称纯碱,是一种白色粉末,可以跟CO2和H2O反应生成NaHCO3,该 反应的化学方程式为____;Na2CO3与稀盐酸反应放出CO2,但实验室却不用这个反应制备CO2,其主要原因可能是____;已知Na2CO3的溶解度比NaHCO3大,那么在饱和的Na2CO3溶液中连续通人CO2,可观察到的现象是____
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Na2CO3+CO2+H2O\u25502NaHCO3,Na2CO3\u4e0e\u7a00\u76d0\u9178\u53cd\u5e94\u901f\u5ea6\u592a\u5feb\uff0c\u4ea7\u751f\u7684CO2\u4e0d\u6613\u6536\u96c6,\u6eb6\

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阅读理解

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    You may not know a lot of people when you start high school. Even if you know some new students, you still feel nervous that you don't know any upperclassmen (高年级学生) and teachers. How are you going to make friends among this sea of unknown faces?

    Most high schools welcome new students before school actually starts. These are helpful not only because you learn your way around the buildings and get to meet some of your teachers, but also because you get to meet new students. That way, when you show up on your first day of school, you may already recognize a few familiar faces.

    When you talk to people, you'll probably find that a lot of them are feeling just like you. They're all new to the school and don't know what to expect. Talking about a common concern with your classmates can help you develop friendships.

    The work in high school is something freshmen are probably worried about. The work in high school builds on what you learned in middle school, giving you a more advanced knowledge of many subjects. So you may find you have more work to do or that it's a bit more challenging (有挑战性的). If you ever find your work too difficult, teachers can give you extra help.

    High school also has more activities after class than middle school, such as clubs, music and theater groups and sports teams. This is a good time to explore your interests and try new things.

    Middle school taught you the basics of academics, time management, and social skills while providing you with a little extra support and guidance. High school gives you the chance to learn how to be more independent (独立的) and responsible (有责任的).