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
2023-08-11
23
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 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] 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(即第8句)就是monocular vision的定义,很明显,选项C为本题答案。首段第7句表明翠鸟在水里能看得清楚,不会像人类那样远视,是因为它眼睛里有两个凹窝区域,并非因为它具有单眼视觉,因此选项A和B都不正确;根据该段第10句可知两个凹窝区域同时发挥作用才能使翠鸟把目光聚焦到猎物身上,因此选项D不正确。
转载请注明原文地址:https://tihaiku.com/zcyy/2917913.html
相关试题推荐
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcen
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcen
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcen
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcen
[originaltext]Ihopeyouhaveallfinishedreadingtheassignedchapteron
Educationofexceptionalchildrenmeansprovisionofspecialeducationalserv
Educationofexceptionalchildrenmeansprovisionofspecialeducationalserv
Educationofexceptionalchildrenmeansprovisionofspecialeducationalserv
Educationofexceptionalchildrenmeansprovisionofspecialeducationalserv
Educationofexceptionalchildrenmeansprovisionofspecialeducationalserv
随机试题
[audioFiles]audio_eufm_j01_323(200910)[/audioFiles]A、Shefeelsfine.B、Shefeel
Let’strytofindoutwhygettingfiberfromwholefoodsisimportantfora
从技术角度看,( )不是云计算所采用的关键技术方法。A.从强调单机的性能(Sc
在某路由器上查看路由信息,结果如下所示。其中表示“S”表明这条路由是( )。
借贷记账法的理论依据是( )。A.借贷平衡 B.有借必有贷 C.复式记账法
化生"涎"的脏腑是A、肾 B、肺 C、脾 D、肝
某甲等30名律师各出资100万元合伙设立了特殊的普通合伙律师事务所——顶呱呱律师
国务院发布的《财务会计报告条例》的法律地位低于全国人大常委会通过的《会计法》。(
防坠安全器是防止吊笼坠落的机械式安全保护装置。用于施工升降机,其作用是(
一台单相变压器二次侧开路,若将其一次侧接入电网运行,电网电压的表达式为U1=U1
最新回复
(
0
)