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
2012-10-11
30
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 (视锥细胞) 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 number of letter he reads
C、the distance he stands away from the chart
D、the speed at which he recognizes the letters
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,由此可确定A为本题答案。
转载请注明原文地址:https://kaotiyun.com/show/cGb7777K
0
大学英语六级
相关试题推荐
A、Coupleslivingtogether.B、Gaycouples.C、Thedivorced.D、Thewidowed.D细节辨认题。本题可采用排除法。文中提到他的研究与现实已经不相符合,因为他的三种分类不包括同居者、同性恋伴侣、
A、Ithelpsimprovethephysicalhealth.B、Itisgoodforasoundsleep.C、Ithelpsdevelopmentaltoughness.D、Ithelpslosewei
WhenToyotaMotorCorp.movedoneofitsdivisionsintoanenvironmentallyfriendly,or“green”,buildinginTorrancethreeyears
WhenToyotaMotorCorp.movedoneofitsdivisionsintoanenvironmentallyfriendly,or“green”,buildinginTorrancethreeyears
Scientistshavedevelopedacomputerisedmind-readingtechniquewhichletsthemaccuratelypredicttheimagesthatpeoplearelo
Ibelievelisteningispowerfulmedicine.Studieshaveshownittakesaphysicianabout18secondstointerruptapatient
America’s-mostpopularnewspaperwebsitetodayannouncedthattheeraoffreeonlinejournalismisdrawingtoaclose.TheNewY
America’s-mostpopularnewspaperwebsitetodayannouncedthattheeraoffreeonlinejournalismisdrawingtoaclose.TheNewY
Asthelecturerhassaid,talentisonething,whileits______expressionisanother.
随机试题
以下哪种激素不由卵巢分泌
特发性功能性低血糖症重症肝炎
以下是冠心病的危险因素,除了( )。
某作家写作的一本书稿出版,取得稿酬收入30000元。其应纳个人所得税为()元。
对会议文件校对时,只有认真检查(),才能杜绝差错。
以某种教学理论为指导,以一定的教学实践为基础形成的,教学活动各个成分按照一定的要求和程序整合而成的,比较固定的和具有典型性的教学实践形式是()。
小明对读书兴趣很深,周末里他想和其他同事一起搞个读书party,但是他事先没有约好同事,他打算发个短信约同事一起参加他的读书活动,请你帮他编辑短信发给他的同事,要求:语言优美引人,读来深切感人,在轻松活泼的气氛中表达出读书的重要。
私营老板张某从税务机关领购增值税专用发票后,将其中的40余张先后卖给他人,后来又购买了500张伪造的增值税发票并转手卖给他人,张某的行为构成()。
2013年我国社会保险工作深人开展,社会保障体系建设取得重大进展。全年五项社会保险(含城乡居民基本养老保险)基金收入合计35253亿元,比上年增长4514亿元,增长率为14.7%。基金支出合计27916亿元,比上年增长4585亿元,增长率为19.7%。
以下程序运行后,消息框的输出结果是a=sqr(3)b=sqr(2)c=a>bMsgBoxc+2
最新回复
(
0
)