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问题 选择题

某电台现录制好10首曲目，其中美声唱法2首，民族唱法4首，通俗唱法4首.拟分两期播出，每期播放其中5首，要求三种唱法每期都有，通俗唱法曲目不得相邻，且第一期的最后一首曲目必须是美声唱法. 则不同的编排方法种数为

A．40320

B．80640

C．35712

D．71424

答案

答案：D

根据题意，分析可得，在第一期的前四个曲目中，要有两个或三个是两个是民族唱法，据此分两种情况讨论，①第一期中安排两个曲目民族唱法，②第一期中安排三个民族唱法，由分步计数原理可得每种情况的安排方法数目，进而由分类加法原理计算可得答案．

解：根据题意，分析可得，在第一期的前四个曲目中，要有两个或三个是民族唱法，

则分两种情况讨论：

①第一期中安排两个曲目民族唱法，则先排这两个唱法，再在其隔出的三个空位上安插通俗唱法，

此时第二期中先排美声唱法和民族唱法，再在其隔开四个空位上安插剩下的两个通俗唱法，

其方法数；

②第一期中安排三个民族唱法，再在其隔开的四个位置上安插一个通俗唱法，

此时第二期中先排剩下的一个民族唱法和美声唱法，在隔开的三个位置上安排剩下的三个通俗唱法，

其方法数．

所以总的编排方法有62208+9216=71424（种），

故选D．

阅读理解
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      Twentieth Century Inventions
●●●1903-The first flight succeeded.                                        


       In 1900, Wilbur Wright said flight was possible for man. After much work he and his brother
Orville Wright made this dream come true.
       On December 17, 1903, the brothers made the first successful airplane flight on a windy beach
at Kitty Hawk, North Carolina. The brothers’ plane flew 120 feet. Although the flight lasted only
12 seconds, it moved the course of history in a new direction. 
●●●1935-Nylon was invented. 
                                          
       In 1928, a new chemical lab was opened to make a kind of man-made materials. Wallace Carothers
took part in the team when he was 32 years old.
       In 1934, he made fibers (纤维), but the fibers were quite weak. He didn’t give up. After many
experiments, he produced the long and strong fibers in 1935. They named the fibers "nylon".
Carothers was very satisfied with his work.
       Nylon hit the markets in 1939, and quickly became a replacement of silk. But it was a pity that he
didn’t see the wide use of his invention. He died in April, 1937.
●●●1968-The computer mouse was first shown in public. 
                                            

       As a graduate student, Douglas Engelbart began to imagine ways in which all sorts of information
could be on screens.   
       In 1964, Douglas Engelbart made the first computermouse. The computer mouse had a wooden
shell with two metal wheels.   
       In 1968, the first computer mouse appeared in public. It was named "mouse" because a tail came
out at the end. In later years, the computer mouse became more and more important.   
       Douglas Engelbart changed the way that computers worked.   
       Now computer mice are becoming increasingly useful. And there are many different shapes of
computer mice in the world.                                          
根据文章内容，完成下列表格。
1. ___________InventionTimeInfluence
Wilbur Wright and his brotherairplane19032.________________________________
Wallace Carothersnylon19353. ________________________________
Douglas Engelbart4. ___________19645. ________________________________
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单项选择题

根据印件排列套色顺序，如果印件有平网和实地，一般地，（）。

A、实地先印，平网图文后印；

B、平网图文先印，实地后印；

C、没有区别
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