已知：a＋b＝m，ab＝－4, 化简（a－2）（b－2）的结果是

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    “Dreams may be more important than sleep. We all need to dream” some scientists say. Dreams take up about one quarter of our sleeping time. People have several dreams each night.

    Dreams are like short films. They are usually in color. Some dreams are like old films. They come up over and over again. That may be the dreamer worrying about something. Dreaming may be a way of trying to find an answer.

    Some people get new ideas about their work from dreams. They may have been thinking about their work all day. These thoughts can carry over into dreams.

    Too much dreaming can be harmful. The more we sleep, the longer we dream. The mind is still at work when we dream. That is why we may have a long sleep and still tired after waking up.

天气预报说，在今后的三天中，每一天下雨的概率均为40%．用设计模拟试验的方法求这三天中恰有一天下雨的概率，利用计算器或计算机可以产生0到9之间取整数值的随机数，我们用1，2，3，4表示下雨，用5，6，7，8，9，0表示不下雨，这样可以体现下雨的概率是40%，因为是三天，所以每三个随机数作为一组，例如，产生了20组随机数：907，966，191，925，271，932，812，458，569，683，431，257，394，028，556，488，720，123，536，983，则得到三天中恰有一天下雨的概率近似为（  ）

国际竞争实质上是综合国力的竞争，综合国力中的决定性因素是（         ）

已知命题，使 命题，都有给出下列结论：
① 命题“”是真命题            ② 命题“”是假命题
③ 命题“”是真命题；        ④ 命题“”是假命题      
其中正确的是