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.

从1、2、3、4、5、6、7、8、9、10这十个数中随机选一个数替代二次根式$\sqrt{x^2-21}$中的字母x使所得二次根式有意义的概率是 ____．

阅读下文，回答问题

粗鄙的暴发户审美充斥着我们的社会

冯骥才

    在北欧，尤其是奥斯陆的大街上，你会感到城市有一种非常舒服的整体性。它没有历史与现代的断裂与分离，而是和谐地浑然一体。这不仅是建筑外部，连建筑内部乃至家具风格也是一样。今天的他们依旧喜欢用新鲜的原木把屋顶装饰得像昔时的农舍，喜欢木头立柱，喜欢没有花纹雕饰的桌椅，喜欢用光洁的木板组合起来的衣柜与书架；但这不是不动脑子地去模仿传统，而是加进去一种后工业时代崇尚的简约美与现代科技能力包括精细的切割与抛光的技术，而使其成为现代审美中一种自己的文化主体元素。他们已经成功地将自己即北欧传统审美的简朴转化为现代审美的简约。

    中国就麻烦多了。自汉唐以来，中原汉文化的审美似乎一贯而下。特别是明代的审美雍容大气、敦厚沉静，从中可以清晰看到汉之博大与唐之沉雄。然而到了清代，入主中原的满族皇帝们对生活文化表面化奢华的欲求，驱使整个社会的审美发生变异。特别是乾隆盛世，审美的繁缛与炫富感走到极致，完全脱离传统审美的厚重与含蓄。可是到清代中期之后，国力的衰败便使这种奢华的追求无法企及而日渐粗鄙，审美能力和审美标准遭到破坏。此后则是外来文化的冲击，以及在“不爱红装爱武装”时代，国民的美育和审美品格已不被提倡。当整个社会由传统的农耕社会转向现代的工业社会时，我们已经无所依据和无所凭借。社会审美像没头苍蝇乱撞。或是呆头呆脑的仿古，或是跟着洋人亦步亦趋地做“现代秀”。如何在审美上从传统向现代过渡，成了当代文化的大难题之一。没有现代审美，也就提不到真正意义上的现代文化。

    而北欧人从传统到现代的审美过渡，不是听凭自然，稀里糊涂地完成的。我想它来自两方面。一方面是经过知识界，即建筑界、艺术界、设计师等长期的创造性的努力与探索。另一方面则是公众的认可。因为，只有成为集体审美，才是一种时代的文化特质。

    然而，我们至今还没有把美育列入素质教育；还有，知识界的努力是重要的关键。如果我们只去克隆舶来的“现代”，或者在传统中找卖点，我们自己的现代审美则无法建立起来。我很欣赏奥运会中的中国印、祥云和开幕式中“画卷”的设计，这是一种积极和精心的努力。当然，还嫌太少，还只是在设计范畴的个别成功的范例，更大的文化问题是我们的现代审美。而这种时代审美是不会自动转换与完成的。如果现代文化建立不起来，留下的空白一定会被商业文化所占据。就像当前充斥我们社会的粗鄙又浮躁的“暴发户审美”。

(有删节)

掉在水平地面上的弹性小球会跳起，而且弹跳的高度会越来越低。下图所示是小球弹跳的频闪照片，小球在1、2位置的高度一样。下面说法正确的是(  )