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
2021-06-15
38
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 mean 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.
Monocular vision enables the kingfisher to______.
选项
A、avoid farsightedness
B、be able to see underwater
C、move one eye at a time
D、focus its eyes on the prey
答案
C
解析
根据文中第一段的“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.”可知,其中一个凹窝让飞翔在空中的翠鸟每次用一只眼睛扫视水下的情况,这被称为单眼视觉。据此可知,单眼视觉让翠鸟能够一次转动一个眼睛,C项正确。
转载请注明原文地址:https://kaotiyun.com/show/0CTO777K
0
考博英语
相关试题推荐
ForthepeoplewhohavenevertraveledacrosstheAtlanticthevoyageisafantasy.Butforthepeoplewhocrossitfrequentlyo
The______questioninthiscaseiswhethertheaccusedhadamotiveforthiscrimeornot.
Thequestionofwhetherwarisinevitableisonewhichhasconcernedmanyoftheworld’sgreatwriters.Beforeconsideringthis
Wewerepleasedtonotethattheearlymorningdeliverydidn’t______tothetrafficjamofthebusycity.
Thedevelopmentofwritingwasoneofthegreathumaninventions.Itisdifficult【C1】______manypeopletoimaginelanguagewitho
Wewillalsoseea______increaseinthenumberoftelevisionsperhousehold,assmallTVdisplaysareaddedtoclocks,coffeem
Thewitness’saccount______closelytothepoliceman’sobservations.
Tostem(阻止)inflalionthegovernmentissued______onprices.
Reductionsinoverseasgovernmentexpendituretookplace,but______andmoregraduallythannowseemsdesirable.(2007年中国科学院考博试题)
Thebraincentersthatprocessnumbersseemtobedifferentforexactand______calculations.
随机试题
下列各项费用中,不属于分部分项工程费的是()。
下列属于严重僵局处理办法的是
对于不同病种,应选定不同心脏超声探查切面,说法正确的是
纤溶酶原活性增高见于
应用激素替代法治疗更年期综合征的适应证是
根据《注册造价工程师管理办法》,造价工程师初始注册的有效期为()年。
“能够及时报告发生火灾的部位”是()。
决定局域网特性的主要技术要素是:网络拓扑、传输介质与______。
在考生文件夹下“sampl.accdb”数据库文件中已建立表对象“tEmployee”。试按以下操作要求,完成表的编辑:设置“年龄”字段的“有效性规则”属性为:人于等于17且小于等于55。
Theshortergrowingseasonsexpectedwithclimatechangeoverthenext40yearswillendangerhundredsofmillionsofalreadypo
最新回复
(
0
)