动物眼中的色彩 在正常人的眼中,能看到红的花,绿的树,蓝的天,白的云……人眼中的世界是多姿多彩五彩缤纷的。那么,大自然中其他动物眼中的色彩是什么样的呢科学家在此方面的研究取得了一定的成果。 研究证实,大多数哺乳动物是色盲。如我们常见的马、牛、羊、狗、猫等,几乎不会分辨颜色,反映到它们眼睛里的色彩,只有黑、白、灰三种颜色,如同我们看黑白电视一样单调。观看斗牛表演时,斗牛士用红色的斗篷向公牛挑战,人们会以为是红色激怒了它,而实际上是因为斗篷在公牛面前不断地摇晃,使它受到烦扰而发怒,如果换上别的颜色的斗篷,公牛也会出现同样的反应。狗也不能分辨颜色,它看景物就像一张黑白照片。狗追捕猎物除了靠四条腿外,主要靠嗅觉和听觉。我们人类的“近亲”猿猴也是色盲,天天过着平淡无奇的灰色生活。田鼠、家鼠、黄鼠、花鼠、松鼠、草原犬等也不能分辨颜色。 值得一提的是斑马,虽然它也是地地道道的色盲,但它却能利用色彩来保护自己。斑马和其他动物混在一起吃草,黑白条纹可以引起注意,因此在出现危险时,只要领头马一动,所有斑马会迅速逃走。当斑马奔跑时,黑白两色条纹的晃动使得捕食动物难以快速测定距离,斑马便可以借机安全逃脱。 但是,并不是所有的哺乳动物都是色盲。鹿对灰色的识别力最强,长颈鹿能分辨黄色、绿色和橘黄色。 鸟类的情况便好多了。除了某些过惯了夜生活的鸟类,如猫头鹰等,因为视网膜中没有锥状细胞,无法认色以外,许多飞禽都有色的感觉。鸟在高空飞行,颜色会帮助它们判断距离和形状,这样它们就能够抓住在高空飞行的虫子,在树枝上轻轻降落。鸟类的辨色能力却也有利于它们寻找配偶。雄鸟常用艳丽的羽毛吸引异性,试想,如果它们感受不到颜色,那雄鸟还有什么魅力呢 多数水生动物都有辨色能力。鲈鱼能感知颜色,生物学家用染成红色的幼虫喂它们,待其习惯后,改用红色羊毛喂它们,鲈鱼竟然照吃不误。龙虾、小虾以及爬行动物里的甲鱼、乌龟和蜥蜴等,也都有色的感觉。 昆虫虽然属低等动物,但是它们的辨色能力却比哺乳动物高明。 据悉,蜻蜓对色的视觉感最佳,其次是蝴蝶和飞蛾。苍蝇和蚊子也能看见颜色。苍蝇最讨厌蓝色,因而不愿接近蓝色的门窗、帐幔。蚊子能够辨别黄、蓝和黑色,并且偏爱黑色。勤劳的小蜜蜂生活在万紫千红的花丛中,却是红色盲,红色和黑色在蜜蜂眼里没有什么区别。蜜蜂能分辨青、黄、蓝三种颜色,但橙、黄、绿在它们看来是一样的,它们也搞不清蓝与紫有何不同。可是,蜜蜂能看见人所看不见的紫外线,并能把紫外线和各种深浅不同的白色和灰色准确地区别开来。 文章的开头为什么写到人眼中多姿多彩的世界
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______,浅草才能没马蹄。(白居易《钱塘湖春行》)
一般认为治疗癫痫持续状态应静脉给予大剂量的苯二氮革类药物,原因是
A. 一次注射后其控制癫痫活动的效果可长达24小时
B. 没有呼吸抑制作用
C. 静脉给药后起效很快
D. 没有致低血压作用
E. 其代谢和清除不依赖肝脏
下列选项是四则“遗失启事”的主要内容,其中表达通顺、得体的一项是______
A. 本人昨天在体育馆遗失一副红色羽毛球球拍,您若及时联系鄙人,不胜感激之至。
B. 昨日本人不慎丢失《随想录》一书于阅览室,期盼拾得者璧还原物,谢谢哟。
C. 本人昨日在图书馆不慎丢失黑色眼镜一副,希望拾得者与我联系,不胜感激。
D. 昨日本人遗失饭卡于学校饮食服务中心,肯请拾者高抬贵手交还,万分感激。
Natural Gas 1. Natural gas is produced from reservoirs deep beneath the earth’s surface. It is a fossil fuel, meaning that it is derived from organic material buried in the earth millions of years ago. The main component of natural gas is methane. 2. The popularity and use of clean natural gas has increased dramatically over the past 50 years as pipeline infrastructure has been installed to deliver it conveniently and economically to millions of residential, commercial and industrial customers worldwide. Today, natural gas services available in all 50 states in the U.S., and is the leading energy choice for fueling American homes and industries. More than 65 million American homes use natural gas. In fact, natural gas is the most economical source for home energy needs, costing one-third as much as electricity. In addition to heating homes, much of the gas used in the United States is used as a raw material to manufacture a wide variety of products, from paint to fibers for clothing, to plastics for healthcare, computing and furnishings. Natural gas is also used in a significant number of new electricity-generating power plants. 3. Natural gas is one of the safest and cleanest fuels available. It emits less pollution than other fossil fuel sources. When natural gas is burned, it produces mostly carbon dioxide and water vapour—the same substances emitted when humans exhale. Compared with some other fossil fuels, natural gas emits the least amount of carbon dioxide into the air when combusted, making natural gas the cleanest burning fossil fuel of all. 4. The United States consumes about one-third of the world’s natural gas output, making it the largest gas-consuming region in the world. The U.S. Department of Energy Information Administration forecasts that natural gas demand will grow by more than 50 percent by 2025. 5. There are huge reserves of natural gas beneath the earth’s surface. The largest reserves of natural gas can be found in Russia, West and North Africa and the Middle East. LNG has been produced domestically and imported in the United States for more than four decades. Today, the leading imports of LNG are Japan, Korea, France and Spain. Paragraph 5 ______.