首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The human criterion for perfect vision is 20/20 for reading the standard lines on a Snellen eye chart without a hitch. The score
The human criterion for perfect vision is 20/20 for reading the standard lines on a Snellen eye chart without a hitch. The score
admin
2017-02-01
81
问题
The human criterion for perfect vision is 20/20 for reading the standard lines on a Snellen eye chart without a hitch. The score is determined by how well you read lines of letters of different sizes from 20 feet away. But being able to read the bottom line on the eye chart does not approximate perfection as far as other species are concerned. Most birds would consider us very visually handicapped. The hawk, for instance, has such sharp eyes that it can spot a dime on the sidewalk while perched on top of the Empire State Building. It can make fine visual distinctions because it is blessed with one million cones per square millimeter in its retina(视网膜). And in water, humans are farsighted, while the kingfisher, swooping down to spear fish, can see well in both the air and water because it is endowed with two foveae(凹窝)-areas of the eye, consisting mostly of cones, that provide visual distinctions. One fovea permits the bird, while in the air, to scan the water below with one eye at a time. This is called monocular vision. Once it hits the water, the other fovea joins in, allowing the kingfisher to focus both eyes, like binoculars, on its prey at the same time. A frog’s vision is distinguished by its ability to perceive things as a constant motion picture. Known as "bug detectors", a highly developed set of cells in a frog’s eyes responds mainly to moving objects. So, it is said that a frog sitting in a field of dead bugs wouldn’t see them as food and would starve.
The bee has a "compound" eye, which is used for navigation. It has 15,000 facets that divide what it sees into a pattern of dots, or mosaic. With this kind of vision, the bee sees the sun only as a single dot, a constant point of reference. Thus, the eye is a superb navigational instrument that constantly measures the angle of its line of flight in relation to the sun. A bee’s eye also gauges flight speed. And if that is not enough to leave our 20/20 "perfect vision" paling into insignificance, the bee is capable of seeing something we can’t—ultraviolet light. Thus, what humans consider to be "perfect vision" is in fact rather limited when we look at other species. However, there is still much to be said for the human eye. Of all the mammals, only humans and some primates can enjoy the pleasures of color vision.
The Snellen eye chart measures one’s eyesight by ____.
选项
A、the number of lines he reads
B、the distance he stands away from the chart
C、the speed at which he recognizes the letters
D、several integrative factors
答案
A
解析
首段第2句中的lines of letters和第3句中的bottom line表明视力的好坏是依靠看到视力表的行数来决定的,选项A为本题答案。首段第2句表明测验视力时距离是预先设定的,选项B不正确;选项C属于无中生有,原文并未提及该内容;文中只提到视力的好坏取决于能看到多少行字母这一因素,并没有提到其他因素,故D项错误。
转载请注明原文地址:https://www.kaotiyun.com/show/xlF7777K
0
大学英语六级
相关试题推荐
MoreandmorepeoplearetakingtheirtabletcomputerstobedtosurftheweborcheckFacebookore-mailsbefore【B1】_____thel
Amajoringredienttotakingthepainoutofastressfuldayatworkisasupportivepartnerathome,anewstudyhas【B1】_____.
Amajoringredienttotakingthepainoutofastressfuldayatworkisasupportivepartnerathome,anewstudyhas【B1】_____.
Americannewspapersarereportingwhatsomepeoplefearistheslowdeathoftheirownindustry.Newspapersearnmostoftheirm
A、Friendsaremorealikebrothersandsisters.B、Itissimpleforfriendstostartaconversation.C、Friendshavesomegenesin
A、Shecannotimproveherselfinthenewjob.B、She’snotsureaboutthejobrequirement.C、Sheisnotsurewhetherthenewjobi
Dohalfofallmarriagesreallyendindivorce?It’sprobablythemostoften【B1】_____statisticaboutmodernlove.Butinanupbe
OxfordUniversityoncefamouslyclaimedtohavebeenfoundedbyAlfredtheGreatinthe9thCentury.Butinfact,theUniversity
DoBritain’sEnergyFirmsServethePublicInterest?[A]Capitalismisthebestandworstofsystems.Lefttoitself,itwillemb
Forthispart,youareallowed30minutestowriteashortessayentitledOnCollegeGraduates’WorkingasVillageOfficials.Yo
随机试题
庄子在《秋水》中以“少仲尼之闻而轻伯夷之义”为论据,是为了论证()
某年9月6日15时,驾驶员A单独驾驶装满液氯的槽罐车驶入某高速公路的X段。17时,槽罐车与驾驶员B驾驶的货车相撞,导致槽罐车破裂,泄漏的液氯导致除驾驶员A以外的两车其他人员死亡。撞车事故发生后,液氯已开始外泄,驾驶员A不顾槽罐车的严重损坏,没有报警也没有采
根据FIDIC《施工合同文件》,关于指定分包商的说法,正确的是()。
我国政府统计系统在业务管理方面实行高度统一的管理,其中,在统计业务上以()领导为主。
那是一个大师辈起的年代,是一个充满______的年代,也是一个尊重知识、______“异端”、追求平等的年代。填入划横线部分最恰当的一项是:
在不同经济发展阶段,经济增长的动力机制是不同的。一个在低收入阶段和中低收入阶段快速增长的发展中国家在进入中高收入阶段后,如果不能适时转换经济增长动力机制,就会面临被“中等收入陷阱”锁定的风险。实证研究表明,制度和原创性技术进步是中等收入国家可持续增长的关键
与积极情感有关系的脑组织是()。
有着悠久历史的肯尼亚国家自然公园以野生动物在其中自由出没而著称。在这个公园中,已经有10多年没有出现灰狼了。最近,公园的董事会决定引进灰狼。董事会认为,灰狼不会对游客造成危害,因为灰狼的习性是避免与人接触的;灰狼也不会对公园中的其他野生动物造成危害,因为公
主机与I/O设备一般利于( )下工作,因此要由接口协调它们工作。
对于GigabitEthernet,1000BASE-LX标准使用的单模光纤最大长度为______。
最新回复
(
0
)