Politeness is a(n) _______phenomenon among all the social groups, but it is marked by different cultures.

____(我) am Sam.

一定量的锌粉和6mol/L的过量盐酸反应，当向其中加入少量的下列物质时，能够加快反应速率，又不影响产生H₂的总量的是
①石墨粉　②CuO　③铜粉　④铁粉　⑤浓盐酸

党的十八届五中全会通过了《中共中央关于制定国民经济和社会发展第十三个五年规划的建议》，该文件广泛听取了各民主党派中央、全国工商联和无党派人士的意见和建议。今年两会上，代表和委员拿到的“十二五”规划纲要草案，就是在该文件的指导下制定的。这说明（    ）

①***是中国特色社会主义事业的领导核心

②我国实行共产党领导的多党合作和政治协商制度

③人大代表是国家权力机关的组成人员，代表人民行使决定权

④人民政协是协商民主的重要渠道，履行参政议政的国家职能

     When you look up into the sky at night, have you ever felt that your eyes are playing tricks on (捉弄) you? It seems that the stars are moving all the time.
      Actually, there is nothing wrong with your eyes. This twinkling effect is called scintillation (交光). Scintillation happens because of air movements in the earth's atmosphere (大气). Light is “bent (弯曲的)” when it travels through different parts of the earth's atmosphere. As the air in the earth's atmosphere is moving all the time, the light from the stars looks as if it is moving too.
    The same thing also happens to things on the ground. On a very hot and shiny day, if you look at the road, the image in the distance is not clear and things move slightly. You can also see the same effect if you drop a rock into water. The rock appears a little unclear under the moving water.
      This twinkling effect causes a lot of problems for astronomers (天文学家) since they cannot observe the stars clearly. A telescope (望远镜) was sent into space so that the air movements in the atmosphere could be avoided (避免). It took a long time to build the space telescope but finally in 1990, a huge space telescope called the Hubble Space Telescope was successfully sent into space. Since then, astronomers have many important observations that have helped people understand space better.
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