这篇英语阅读的答案Zebra’s stripes(条纹) have puzzled scientists around

这篇英语阅读的答案
Zebra’s stripes(条纹) have puzzled scientists around the world for centuries.What is the biological purpose of being covered with in black and white stripes?
There are many theories that try to answer that question .Charles Darwin ,the famous biologist ,thought that Zebra’s stripes were used to attract partners .
Alfred Wallace ,the British naturalist and biologist thought the stripes were camouflage(伪装).They make the zebras hard to see at night and create an optical illusion(视错觉) in the day .This protects them from being hunted by lions and other fierce animals .
But the zebra’s real enemy might be a whole lot smaller .A new study by Tim Caro from the University of California has come up with an entirely new theory on why zebras have stripes .He thinks that their stripes will keep biting flies away from them .
Caro and his colleagues took a different route to other scientists who have studied zebra’s stripes .Instead of looking just at zebras ,he looked at all equids (马科动物)（horses ,zebras and asses）and the different patterns of their stripes.
He found that species (物种）that lives in areas with dangerous flies were more likely to have stripes all over their bodies .Zebras live in Africa ,where biting flies can cause great harm by both passing on diseases and sucking(吸）out dangerous amounts of blood.
Caro is happy that they have answered the question of why zebras have stripes,but now he is left another question:why don’t flies likes stripes
―That’s what happens in science‖,he told The New Yorker magazine .―You answer one question and it leads to six more.‖
( ) 48.According to Tim Caro,zebras have stripes to ___________.
A.protect them from being seen B.attract partners
C.create illusions D.keep biting flies away
( ) 49.Caro and his colleagues got the findings by __________.
A.examining the stripes of zebras B.staying with zebras in Africa
C.observing zebras at night D.studying all animals with stripes
( ) 50.The last sentence suggests that __________.
A.scientists sometimes find it difficult to answer the question
B.people can never really find the answer to the question
C.there are always unknown things for people to study
D.scientists need to answer seven questions to find out the truth
( ) 51.Where can we probably read this passage
A .In a guidebook .B.In a science fiction book
C.In a science magazine .D.In an introduction to a zoo .
D

48.D,keep biting flies away
49.D,studying all animals with stripes
50.C,there are always unknown things for people to study
51.C,In a science magazine .
再问： 第49题的D选项是所有动物，而文章中提到的是所有马科动物，为什么选d
再答： 用排除法，其它三个明显不是。这正是 Caro与众不同之处，他既没有把精力放在条纹本身，也没有一定要与斑马朝夕相处，也没有进行夜观察。这些都是以前研究者的做法。