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
55
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
Itisacontradictionthatinsucharichcountrythereshouldbesomanypoorpeople.
Withinhoursofappearingontelevisiontoannouncetheendofconscription,PresidentJacquesChiracmovedquicklytopreventa
Thedevelopmentofwritingwasoneofthegreathumaninventions.Itisdifficult【C1】______manypeopletoimaginelanguagewitho
Wecannot______ourinfluenceunlesswehaveanorgan.
Agriculturemust,therefore,______workersandsavingstothenewindustrialized,urbanizedsectorsifamoderneconomyistobe
Abortion(堕胎)inBritainisahighly______matter:somearestronglyforit,somearebitterlyagainstit.
Thereishardlyageneralizationthatcanbemadeaboutpeople’ssocialbehaviorandthevaluesinformingitthatcannotbe_____
Duringthepastgeneration,theAmericanmiddle-classfamilythatoncecouldcountonhardworkandfairplaytokeepitselffin
Technically,anysubstanceotherthanfoodthataltersourbodilyormentalfunctioningisadrug.Manypeoplemistakenlybeliev
随机试题
A、多能集落刺激因子B、Ⅱ型干扰素C、肿瘤坏死因子D、IL-1E、肝细胞生长因子能够刺激多能造血干细胞增殖分化的细胞因子是
型式评价结束后,经审查合格的,由__________向申请单位颁发型式批准证书。
《锅炉大气污染物排放标准》未规定排放限值的污染物是()。
下列选项中,( )属于意思表示不真实的民事行为。Ⅰ.恶意串通损害他人利益的行为Ⅱ.以合法形式掩盖非法目的行为Ⅲ.误将赝品作为真品出卖的行为Ⅳ.与他人合伙开设赌场的行为Ⅴ.因,乏威胁而将房屋低于市价过户给威胁人
改革开放以来,我国农村管理体制的一个重大变革就是允许农民()。
下列选项中,取消预科,使大学不再担负普通教育任务的是
[1998年]有人认为,在社会主义现代化建设过程中,只要物质文明搞好了,精神文明自然而然就上去了。试用历史唯物主义关于社会存在与社会意识辩证关系的原理,并结合我国的实际评析上述观点.闸明加强礼会主主义精神文明建设的意义、
有以下程序 #include<stdio.h> #include<string.h> main() {charstr[][20]={"One*World","One*Dream!"},*p=str[1]; printf("%d,",strl
Speaktohimslowly________hemayunderstandyoubetter.
WhenmenreturnedfromWorldWarIIandthepostwar"babyboom"began,Americansbegantomoveingreatnumberstothe【B1】______
最新回复
(
0
)