题干

已知某生产厂家的年利润(单位:万元)与年产量(单位:万件)的函数关系式为,则使该生产厂家获得最大年利润的年产量为

A:13万件

B:11万件

C: 9万件

D:7万件

上一题 下一题 0.0难度 选择题 更新时间:2016-03-07 05:49:53

答案(点此获取答案解析)

C

同类题3

阅读下面的短文,完成后面小题。

《蚊子为什么没有被雨滴砸死之谜》

    ①漫步细雨中对于人们来说,或许是浪漫而惬意的,但对体积微小的昆虫而言,譬如蚊子,雨中漫步简直是一场灾难。一滴雨的重量可达到蚊子体重的50倍之多,人们所谓的毛毛雨,在蚊子看来,不亚于一辆辆甲壳虫汽车从天而降。但是,在这“甲壳虫汽车雨”中,蚊子却能够毫发无损,这是什么原因呢?

    ②为破解这一谜题,美国佐治亚理工学院的胡立德教授与美国疾控中心合作,对雨中飞舞的蚊子进行了高速摄像,以观察蚊子被雨滴击中瞬间的行为。

    ③通过视频,胡立德教授与他的研究小组分析了雨滴击中蚊子不同部位的各种情况,计算出蚊子被雨滴击中的瞬间所受到的作用力,以及其后随雨滴向下移动的距离。他们发现,蚊子并不像人们可能推测的那样去躲避雨滴,也不会因遭到雨滴的冲击而受伤,秘密之一就在于蚊子体重极轻。

    ④原来,蚊子被雨滴击中时并不进行抵挡,而是与雨滴融为一体,顺应它的趋势落下。如果雨滴击中蚊子的翅膀或腿部,它会向击中的那一侧倾斜,并通过“侧身翻滚”的高难度动作,让雨滴从身体一侧滑落;当雨滴正中蚊子身体时,它先顺应雨滴强大的推力与之一同下落,随之迅速侧向微调与雨滴分离并恢复飞行。

    ⑤研究者还发现,当雨滴击中栖息于地面的蚊子时,雨滴的速度在瞬间减小为〇,这时蚊子就会承受相当于它体重10000倍的力,足以致命。当蚊子在空中被击中并采用“不抵抗”策略时,它受到的冲击力就减小为其体重的1/50至1/300,此时,这雨滴就像一根极细小的羽毛压在了蚊子身上——这是蚊子能够承受的

    ⑥虽说蚊子柔弱如风中柳絮会被雨滴砸得摇晃不定,但正是由于它体重极轻,雨滴在与蚊子碰撞的过程中几乎没有减速,它的动能也几乎没有转化为能量击打在蚊子身上,而是让蚊子瞬间加速下降,从而化解了高速下降的雨滴带来的巨大冲击。这就像是“以柔克刚”,达到“四两拨千斤”的效果,小小的蚊子还是个太极高手呢!

    ⑦蚊子在雨中安然无恙的另一个秘密,是覆盖它们全身的细毛具有疏水性。这种防水的细毛使得蚊子与打在它身上的雨滴保持分隔状态,从而使蚊子能够迅速摆脱雨滴重新飞起,在雨滴将它们砸落地面造成致命伤害前成功逃生。

    ⑧胡立德教授的这一发现引起了广泛关注。事实上,这项研究不只是跟蚊子有关。在应对自然之道上,动物往往有着比人类更丰富的经验,它们在千万年的进化过程中拥有了适应生存环境的生理结构和功能。研究动物应对大自然的特殊本领,可为科学家和工程师提供新的设计思想,解决机械技术上的诸多难题——比如,如何更好地设计微型飞行器,让它们能像蚊子这类昆虫一样,在雨中轻盈地飞翔。

同类题4

        Millions of people all over the world use the word OK. In fact, some people say the word is used more often than any other word in the world. OK means all right or acceptable. It expresses agreement or approval.

        ____ Some people say it came from the Native American Indian tribe known as the Choctaw(乔克托语). The Choctaw word “okeh” means the same as the American word “okay”. Experts say early explorers in the American West spoke the Choctaw language in the nineteenth century.

        But many people doubt this. Language expert Allen Walker Read wrote about the word “OK” in reports published in the 1960s. He said the word began being used in the 1830s. ____ Some foreign­born people wrote “all correct” as “o­l­l­k­o­r­r­e­c­t”, and used the letters OK. Other people say a railroad worker named Obadiah Kelly invented the word long ago. They say he put the first letters of his name—O and K—on each object people gave him to send on the train.

        ____ The organization supported Martin Van Buren for president in 1840. They called their group the OK club. The letters were taken from the name of the town where Martin was born—Old Kinderhook, New York.

        Then there is the expression A­OK. It is a space­age expression. It was used in 1961 during the flight of astronaut Alan Shepard. He was the first American to be launched into space. His flight ended when his spacecraft landed in the ocean, as planned. Shepard reported, “Everything is A ­OK.” ____ One story says it was first used during the early days of the telephone to tell an operator that a message had been received.

        There are also funny ways to say okay. ____ These expressions were first used in the 1930s. Today, a character on the American television series The Simpsons says it another way. He says okely­doke.

A.Some people say okey­dokey or okey­doke.

B.Still others say a political organization invented the word.

C.Therefore, it has become popular in that area from then on.

D.But many experts don't agree on what the expression means.

E.Still, language experts do not agree about where the word came from.

F.It was a short way of writing a different spelling of the word “all correct”.

G.However, some experts say the expression did not begin with the space age.