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
2010-11-02
87
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.
How is hawk’s eyesight better than ours?
选项
A、It can identify small items more quickly than we do.
B、It can see at a longer distance than we do.
C、It has more cones in the retina than we do.
D、h has bigger eyes than we do.
答案
B
解析
该句中的can spot a dime和on top of the Empire State Building形象地表明hawk(鹰)能看到距离很远的物件,B为本题答案。
转载请注明原文地址:https://kaotiyun.com/show/OJs7777K
0
大学英语六级
相关试题推荐
Oursleeptimeoverthepastcenturyhasbeen【B1】______byalmost20percent.Generally,adultsneedtosleeponehourfore
Noiseentersourearsaspowerfulwavesofmechanicalenergy.Scientistsmeasuresoundintensityindecibels(db),witheachdou
Wearerapidlyneartheendofthiscourseinthehistoryof【B1】______music.Wehavecoveredseveralcenturiesinaveryshort
Moreandmore,theoperationsofourbusinesses,governments,and【B1】______institutionsarecontrolledbyinformationthatexis
A、Beunabletobreathe.B、Beovercomebypressure.C、Becomespeechless.D、Bescaredbypressure.B综合推断题。文章最后一段介绍了有助于成功的第四个特质,cal
WhyMenandWomenCan’tCommunicate—byDeborahTannen
Notlongago,mosthistorianshadtobetravelers.【C1】______writtenaccountsofhistoricalevents,theyhadtotraveltothepl
A、Itisthrownaway.B、Itisburnt.C、Itisturnedintosomesolidobjects.D、Itisstoredunderground.B选项和方式有关。本题是细节题。从Theres
A、Thetwospeakersareclassmates.B、Themanismajoringinelementaryeducation.C、Thewomanismajoringinelementaryeducatio
Nearlyallsurgicalstuntsstickthemselveswithneedlesand【C1】______instrumentswhileintraining.But【C2】______failtorepo
随机试题
经营战略的实质在于()
Tobeagoodteacher,youneedsomeofthegiftsofagoodactor,youmustbeableto【C1】______theattentionandinterestofyou
下列情况属于结果加重犯的有()。
已知:某公司2011年销售收入为20000万元,销售净利率为12%,净利润的60%分配给投资者。2011年12月31日的资产负债表(简表)如下:该公司2012年计划销售收入比上年增长30%,为实现这一目标,公司需新增设备一台,价值148万元。
A企业注册资本为5000万元,2004年2月10日,甲企业向税务机关报送了该企业2003年度企业所得税纳税申报表,其中产品销售收入净额为2500万元,减除有关的成本、费用、税金、损失后,会计利润总额为625万元,应纳税所得额为625万元,税务机关委托某会计
当前,我国学校教学的基本组织形式是()。
一、注意事项1.申论考试是对考生阅读理解能力、综合分析能力、提出和解决问题能力、文字表达能力的测试。2.仔细阅读给定的资料,按照后面提出的“申论要求”依次作答。二、给定资料1.人民网北京2009年8月25日电:十一届全国人大常委会第十次会议今天下午
WiththeadventoftheInternet,informationcanbespreadwithunprecedentedspeedandhenceitislikelythatpeoplecanmake
Suicide,thenumber-twokillerofcollegestudent,claimsthelivesofapproximately5,000college-agepeopleeachyear.Thatnu
[A]access[B]accordingly[C]advocate[D]automatic[E]contend[F]content[G]enhanced[H]enriched[I]ineffective
最新回复
(
0
)