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
2023-09-04
48
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] 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、It 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://tihaiku.com/zcyy/2984295.html
相关试题推荐
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
PartⅡReadingComprehension(SkimmingandScanning)Directions:Inthispart,y
Byreadingmother’sfacialexpressions,______(我隐约猜到将有不同寻常的事发生).Iguessedvaguel
WhenToyotaMotorCorp.movedoneofitsdivisionsintoanenvironmentallyfr
WhenToyotaMotorCorp.movedoneofitsdivisionsintoanenvironmentallyfr
Scientistshavedevelopedacomputerisedmind-readingtechniquewhichlets
随机试题
Itsuddenly________tomethatsomebodymightbeabletolendusthemoney.A、came
Cricket,althoughlovedbymillionsofpeople,isnotoneoftheeasiestspo
演出策划是指针对演出项目进行组织、创意,实现演出( )和促进演出( )的过程
内部审计业务随其客观性程度的变化而变化。以下哪一项最有可能具备客观性?()A
拱桥按结构受力可分为无铰拱、二铰拱及三铰拱桥,下列关于拱桥的构造要求说法正确的是
(2017年真题)法定资产评估业务的评估档案保存期限应当不少于()。A.10年
中药注射剂所用安瓿的处理工艺为A.切割→圆口→干燥→洗涤→灭菌B.切割→圆口→灌
患者取药时,药师进行用药指导的主要目的是使患者A:知道拿到的药品是否会发生不良反
引起机械性肠梗阻最常见的原因是A:腹膜后巨大血肿 B:肠壁肿瘤 C:肠道蛔虫
(2019年真题)根据会计法律制度的规定,下列各项中,属于会计工作岗位的有(
最新回复
(
0
)