如图,CD,EF表示高度不同的两座建筑物,已知CD高15米,小明站在A处,视线越过CD,能看到它后面的建筑物的顶端E,此时小明的视角∠FAE=45°,为了能看到建筑物EF上点M的位置,小明延直线FA由点A移动到点N的位置,此时小明的视角∠FNM=30°,求AN之间的距离．

取一支蜡烛，用小刀切下一块，这说明蜡烛的硬度____，将其放入水中，蜡烛浮在水面上，这说明蜡烛的密度比水____，将蜡烛点燃，观察到蜡烛的火焰分____、____、____三层．把火柴梗放在火焰上1秒后取出，可以看到火柴梗____的部分最先碳化，这说明蜡烛火焰的____温度最高．将一只干燥的烧杯罩在蜡烛火焰的上方，烧杯内壁出现了____，片刻后取下烧杯，迅速向烧杯内倒入少量澄清的石灰水，振荡，澄清的石灰水变____，这说明蜡烛燃烧后生成了____和____．

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    Everybody, welcome to ____(we) company. I am Luisa, Director of the department. Let me say something to you all. The starting of work can be exciting on the hand, and can also be ____(worry) on the other. No matter what your future job is, you will have to work with others. Leaning to get on well with others must come first,____ (include) all staff in the company and our ____ (custom).

    And secondly, right after my introduction, spend some time reading the introduction of our company and get to know the people in your office and find out ____ the company is like. This afternoon you can walk around our workshops and know ____ (much) about the products. No one is allowed ____ (leave) the company before 5:30 pm. By the way, lunchtime ____ (come) at 11:50 and it's free ____ charge.

    Remember: Learning is so important ____ it can change your future life.

This is what I'd like to say to you at the moment. If you still have any question, please come to my office. Thank you.

China’s economic development has made      rapid progress in the past years and young people have made      great contribution to this progress.

已知氘核的质量为2.0136U，中子的质量为1.0087U， He核的质量为3.0150U，两个速率相等的氘核对心碰撞聚变成 He并放出一个中子，释放的核能也全部转化为机械能．（质量亏损为1U时，释放的能量为931.5MeV．除了计算质量亏损外， He的质量可以认为是中子的3倍．）