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
2024-04-13
12
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] The Snellen eye chart measures one’s eyesight by ____.
选项
A、the number of lines he reads
B、the distance he stands away from the chart
C、the speed at which he recognizes the letters
D、several integrative factors
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,选项A为本题答案。首段第2句表明测验视力时距离是预先设定的,选项B不正确;选项C属于无中生有,原文并未提及该内容;文中只提到视力的好坏取决于能看到多少行字母这一因素,并没有提到其他因素,故D项错误。
转载请注明原文地址:https://tihaiku.com/zcyy/3553395.html
相关试题推荐
AnneHechehasprovenherselfanexceptionalactressinfilm,televisionand
AnneHechehasprovenherselfanexceptionalactressinfilm,televisionand
AnneHechehasprovenherselfanexceptionalactressinfilm,televisionand
清明是中国的二十四节气(the24seasonaldivisionpointsinChina)之一,每年4月4—6日。节日过后,温度将会上升
[originaltext]W:Withusnow,isMalcolmBricklin,CEOofVisionaryVehicles.M:
[originaltext]W:Withusnow,isMalcolmBricklin,CEOofVisionaryVehicles.M:
[originaltext]W:I’vejustfinishedreadingSteve’slistofwaysofmotivatinge
[originaltext]W:I’vejustfinishedreadingSteve’slistofwaysofmotivatinge
[originaltext]W:I’vejustfinishedreadingSteve’slistofwaysofmotivatinge
[originaltext]Domesticdogscanperceiveimagesontelevisionsimilarlyto
随机试题
Anintellectualbreakthrough,______,doesnotautomaticallyensurethatthetra
BetterKnownasMarkTwainThisremarkableman
EmilyDickinsonwasdifferentfromotherwomenofhergenerationinthatshe
以注册商标权出质的,质权自()生效。A.出质合同签订之日 B.商标注册证交付质
鞍区CT扫描技术不包括A.疑颅内肿瘤侵入鞍区时,须加做常规头部扫描 B.横断位
英雄烈士的()受法律保护。A.姓名 B.肖像 C.名誉 D.荣誉
补体C3缺陷会导致A.发热B.水肿C.红斑狼疮D.严重感染E.肾小球肾炎
A.C-α-醇酮基B.羧基C.β-羟基所形成的丙酸酯D.甲酮基E.酚羟基丙酸睾酮
左图为给定的多面体,从任意角度观看,下列哪一项不可能是该多面体的视图? A.如
投资项目决策分析与评价的基本要求包括贯彻落实科学发展观、资料数据准确可靠和()
最新回复
(
0
)