问题
选择题
有5个不同的小球,装入4个不同的盒内,每盒至少装一个球,共有（ ）不同的装法.
A．240
B．120
C．600
D．360
答案
答案：A
题目分析：先将5个小球分成4组，共
种分法，再将4组分配到4个不同的盒子里共有
种方法，所以共
种分配方案
点评：较复杂的排列组合问题一般都采取先分组再分配，结合分步计数原理求解
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有5个不同的小球,装入4个不同的盒内,每盒至少装一个球,共有（ ）不同的装法.
A．240
B．120
C．600
D．360
答案：A
题目分析：先将5个小球分成4组，共种分法，再将4组分配到4个不同的盒子里共有种方法，所以共种分配方案
点评：较复杂的排列组合问题一般都采取先分组再分配，结合分步计数原理求解
We took the bus from the suburb every early morning that summer 3 years ago. One of the passengers was a small 36 man who took the bus to the centre for senior citizens every morning. He walked with a stoop (佝偻) and a sad look on his face when he, with some difficulty, 37 the bus and sat down alone behind the driver. No one ever paid very much attention to him. Then one 38 morning he said good morning to the driver and smiled before he sat down. The driver 39 guardedly. The rest of us were silent. The next day, the old man boarded the bus energetically, 40 and said in a loud voice: “And a very good morning to you all!” Some of us looked up, amazed, and murmured “Good morning,” 41 . The following weeks we were more alert (留意的). Our friend was now dressed in a nice old suit and a wide out-of-date 42 . The thin hair had been carefully combed. He said good morning to us every day and we 43 began to nod and talk to each other. One morning he had a bunch of wild flowers in his hand. The driver 44 smilingly and asked:“Have you got yourself a girlfriend, Charlie?”and he nodded shyly and said yes. The other passengers 45 and clapped at him. Charlie bowed and waved the 46 before he sat down on his seat. Every morning after that Charlie always brought a flower. Some of the 47 passengers began bringing him flowers for his bouquet(花束). The summer went by, and 48 was closing in, when one morning Charlie wasn't waiting at his usual 49 . When he wasn't there the next day and the day after that, we started wondering if he was sick or — 50 — on holiday somewhere. One day, we learned from the staff working in the centre for senior citizens that the elderly 51 was fine, but he hadn't been coming to the 52 that week. One of his very close friends had died at the weekend. They 53 him back on Monday. How silent we were the rest of the way to work. The next 54 Charlie was waiting at the stop, stooping a bit more, a little bit more grey, and without a tie. He seemed to have shrinked（缩小）again. Inside the bus was a 55 . All of us sat with our eyes filled with tears and a bunch of wild flowers in our hands.
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