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
11
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.
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
首段第9句中的this表明前一句就是monocular vision的定义,选C。
转载请注明原文地址:https://kaotiyun.com/show/MGb7777K
0
大学英语六级
相关试题推荐
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,youwillhave15minutestogooverthepassageq
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,youwillhave15minutestogooverthepassageq
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,youwillhave15minutestogooverthepassageq
A、Henolongerwatchesmuchtelevision.B、Hepreferscomediesfromthesixties.C、Hethinkscomedieshaven’timprovedforyears.
Byreadingmother’sfacialexpressions,______(我隐约猜到将有不同寻常的事发生).
A、Heisweakinhealth.B、Hehascaughtacold.C、Heisverycareless.D、Heisseriouslyill.A听音时要抓住关键词组alittleunderthewea
A、Notclearlyspecified.B、Notlikelytobemet.C、Reasonableenough.D、Apparentlynonexistent.B推理判断题。对话结尾处女土说Ithinkyou’reas
America’s-mostpopularnewspaperwebsitetodayannouncedthattheeraoffreeonlinejournalismisdrawingtoaclose.TheNewY
America’s-mostpopularnewspaperwebsitetodayannouncedthattheeraoffreeonlinejournalismisdrawingtoaclose.TheNewY
Asthelecturerhassaid,talentisonething,whileits______expressionisanother.
随机试题
下列有关生活中常见的物理常识的叙述正确的是:
带传动的优点有()。
会计核算的信息质量要求有()。
企业开具增值税专业发票的时限为()。
根据物权法律制度的规定,下列各项中,属于他物权的有()。
C公司计划对行政部经理这一职位进行内部公开竞聘。请回答以下问题:在正式竞聘之前,人力资源部需要做好哪些工作?
为发扬教育改革的精神,某学校决定开设校本课程。下列做法正确的是()。
A、 B、 C、 D、 B各图形内圆的数量依次减少:6,5,4,3,2,1;直线或线段数依次增加:0,1,2,3,4,5,故只有B符合题意。
最近南方某保健医院进行为期15周的减肥试验,参加者平均减肥10公斤。男性参加者平均减肥14公斤,女性参加者平均减肥8公斤。医生将男女减肥差异归结为大部分男性参加者减肥前体重比女性参加者重。从上文可推出以下哪个结论?()
YoucanseeManykindsofanimalsthere.YoucanWriteordrawthingsonitinschool.
最新回复
(
0
)