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
2018-08-25
67
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://kaotiyun.com/show/sLH7777K
0
大学英语六级
相关试题推荐
A、HewantsothercountriestounderstandtheU.S.B、Hecallsonsomebigcompaniestocareaboutclimate.C、Hecallsonpeoplei
A、IthasthehighestwatercleanlinessstandardinEurope.B、IthasthebestnaturalswimmingpoolinEurope.C、Ithasthebest
A、Becauseitcosts$77billiontodevelopfurther.B、Becauseitevenputsdatainofflinedevicesindanger.C、Becauseitaims
A、BecauseCO2accountsfor65percentofclimatechange.B、BecausethelevelofCO2emissionshasreachedarecordhigh.C、Becau
FrustratedwithdelaysinSacramento,BayAreaofficialssaidThursdaytheyplannedtotakemattersintotheirownhandstoregu
Smokersinthe"landofthefree"arefindingthemselvesincreasinglylessfreetopursuetheirhabit.NewYorkCityofficialsa
Smokersinthe"landofthefree"arefindingthemselvesincreasinglylessfreetopursuetheirhabit.NewYorkCityofficialsa
Lackofsleepmakesyougainweightandraisesyourriskforheartdiseaseanddiabetes,apartfromresultingin【C1】______vision
随机试题
护士长在管理过程中,遇到问题时经常发动护士们共同讨论,共同商量,集思广益,然后决策,并要求病房护士每个人各尽所能,各施其长,分工合作,这种领导作风属于
城镇燃气管道系统由各种压力的燃气管道组成,其组合形式有()系统。
背景某工程,建设单位与施工单位按照《建设工程施工合同(示范文本)》签订了施工承包合同。合同约定:工期6个月;A、B工作所用的材料由建设单位采购;合同价款采用以直接费为计算基础的全费用综合单价计算;施工期间若遇物价上涨,只对钢材、水泥和集料的价格进
合同控制的作用之一是了解合同的实施情况,找出偏离,以便及时采取措施,调整合同实施过程,达到( )。
国家对事业单位工作人员实行()。
BeingpluggedintoaniPodisafeatureofadolescence.Anewstudysuggeststhatteenswhospendtoomuchtimelisteningtomus
下面有关计算机的叙述中,正确的是( )。
Somepeoplebelievethatcorporationshavearesponsibilitytopromotethewell-beingofthesocietiesandenvironmentsinwhich
"Whatdoesthemiddlemandobutaddtothepriceofgoodsintheshops?"Suchremarksareaimedattheintermediateoperationsb
【B1】【B3】
最新回复
(
0
)