首页
登录
职称英语
The human criterion for perfect vision is 20/20 for reading the standard lin
The human criterion for perfect vision is 20/20 for reading the standard lin
游客
2024-05-16
11
管理
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. [br] 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://tihaiku.com/zcyy/3600560.html
相关试题推荐
OKimiyukiSudashouldbeaperfectcustomerforJapan’scarmakers.He’sayo
OKimiyukiSudashouldbeaperfectcustomerforJapan’scarmakers.He’sayo
Livingstandardshavesoaredduringthe21stcentury,andeconomistsexpect
Livingstandardshavesoaredduringthe21stcentury,andeconomistsexpect
Livingstandardshavesoaredduringthe21stcentury,andeconomistsexpect
Livingstandardshavesoaredduringthe21stcentury,andeconomistsexpect
Livingstandardshavesoaredduringthe21stcentury,andeconomistsexpect
Afewyearsagoitwas【B1】______tospeakofagenerationgap,adivisionb
Afewyearsagoitwas【B1】______tospeakofagenerationgap,adivisionb
Afewyearsagoitwas【B1】______tospeakofagenerationgap,adivisionb
随机试题
[img]2014m9x/ct_egreqj_egreqbj_0001_20148[/img][br]CInthisquestionyouarea
[originaltext]M:Ican’treachTom.There’sabusysignal.W:Thenhangupand
注射于表皮与真皮之间的给药途径为A.静脉注射B.椎管注射C.肌内注射D.皮下注射
强心苷通过水解反应常得到脱水苷元的反应是A:温和的酸水解 B:强烈的酸水解
语文教师在教古诗《春晓》时,小龙禁不住发问:“老师,诗人春天好睡觉,连这都不晓得
在制定国际劳动公约的过程中,将公约草案提交大会投票表决,表决结果赞成票达到(
夏普比率的不足之处在于( )。A.未考虑收益的平均波动水平 B.只考虑了最大
上颌第一磨牙最小的牙尖是哪一个A.远中颊尖 B.远中尖 C.远中舌尖 D.
脂肪动员的关键酶是A:激素敏感性三酰甘油酶 B:酯酰CoA脱氢酶 C:二酰甘
关于承揽合同解除的说法,正确的是( )。A.承揽人未经定作人同意将其承揽的主要
最新回复
(
0
)