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汽车防冻液

     汽车在行驶时,发动机的温度会升得很高。为了确保安全,可用水循环进行冷却。实际上,水中往往还要加入不易挥发的防冻液(原液),加入防冻液后的混合液冬天不容易凝固,长时间开车也不容易沸腾。

    有关资料表明,防冻液与水按不同的比例混合,混合液的凝固点、沸点不同,具体数值参见下表(表中防冻液含量是指防冻液在混合液中所占体积的百分比)。

在给汽车水箱中加防冻液时,宜使混合液的凝固点比本地常年最低气温低10~15℃.考虑到混合液比热容的减小会影响散热效果,因此,混合液中防冻液的含量不宜过高。

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    I told my friend Graham that I often cycle two miles from my house to the town centre but unfortunately there is a big hill on the route. He replied, "You mean fortunately." He explained that I should be glad of the extra exercise that the hill provided.

    My attitude to the hill has now changed. I used to complain as I approached it but now I tell myself the following. This hill will exercise my heart and lungs. It will help me to lose weight and get fit. It will mean that I live longer. This hill is my friend. Finally I comfort myself with the thought of all those silly people who pay money to go to a gym and sit on stationery exercise bicycles when I can get the same value for free. I have a smile of satisfaction as I reach the top of the hill.

    Problems are there to be faced and overcome. We cannot achieve anything with an easy life. Helen Keller was the first deaf and blind person to gain a university degree. Her activism and writing proved inspirational. She wrote, "Character cannot be developed in ease. Only through experiences of suffering can the soul be strengthened, vision cleared, ambition inspired and success achieved."

    One of the main determinants of success in life is our attitude towards adversity (逆境). From time to time we all face hardships, problems, accidents and difficulties. Some are of our making but many are no fault of our own. While we cannot choose the adversity, we can choose our attitude towards it.

    Douglas Bader was 21 when in 1931 he had both legs cut off following a flying accident. He was determined to fly again and went on to become one of the leading flying aviators in the Battle of Britain with 22 aerial victories over the Germans. He was an inspiration to others during the war. He said, "Don't listen to anyone who tells you that you can't do this or that. That's nonsense. Make up your mind, you'll never use crutches (拐杖) or a stick, and then have a go at everything. Go to school, and join in all the games you can. Go anywhere you want to. But never, never let them persuade you that things are too difficult or impossible."

    The biographies (传记) of great people are full of examples of how they took steps to overcome the difficulties they faced. The common thread is that they did not become depressed. They chose their attitude. They chose to be positive. They took on the challenge. They won.

    Nevertheless, there is still the problem of how you change your attitude towards adversity.