题干

在实验室中制取88g二氧化碳,需要多少克碳酸钙跟盐酸反应?若改用杂质含量为20%的石灰石与盐酸反应(杂质不与盐酸反应),徐这种石灰石多少克?

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解:设需要碳酸钙的质量为X,

CaCO3+

2HCl═

CaCl2+H2O+

CO2

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    If you are like most international students, you are probably pretty comfortable reading and writing in English. ____Below are some tips to help you to improve your conversational skills.

    Make friends with American students. Many international students end up making friends with a lot of—or only—other international students.____ Hanging out with natives not only naturally pushes you to improve your spoken English, but also helps you pick up cultural and social information.

    Learn from American friends. Tell your American friends that you are trying to improve your listening and speaking skills, and would like them to help you. If you pronounce a word incorrectly, or misuse an idiom, you ask them to guide you. ____

    Increase your knowledge. ____ If you have been exposed to topics that are likely to be discussed in conversation, you have a much better chance of understanding people when they talk, and of being able to express yourself well.

    ____ If you have to explain something to someone, you have a strong motivation to pronounce everything as well as you can, and find other ways to explain yourself. Finally, this becomes a good habit. Many people have asked me how I learned to speak English fluently, and I owe most of it to my years of being a math teacher in college for years.

A. It is bad for them to do that.

B. You will make progress this way.

C. If possible, become a teacher at your school.

D. It's a win-win opportunity for international students.

E. Keep up with news and watch popular shows and movies.

F. Explaining everything in a different way counts.

G. You may have trouble in listening and speaking in the language, however.