It'soneofourcommonbeliefsthatm-考网

It's one of our common beliefs that mice areafraid of cats.Scientists have long known that even if a mouse has never seena cat before,it is still able to detect chemical signals released from the catand run away in fear.This has always been thought to be something that ishard-wired into a mouse's brain.

But now Wendy Ingram,a graduate student at theUniversity of California,Berkeley,has challenged this common sense.She hasfound a way to"cure"mice of their inborn fear of cats by infectingthem with a parasite,reported the science journal Nature.

The parasite,called Toxoplasma gondii,might soundunfamiliar to you,but the shocking fact is that up to one-third of peoplearound the world are infected by it.This parasite can cause different diseasesamong humans,especially pregnant women--it is linked to blindness and thedeath of unborn babies.

However,the parasite's effects on mice are unique.Ingram and her team measured how mice reacted to a cat's urine before and afterit was infected by the parasite.They noted that normal mice stayed far awayfrom the urine while mice that were infected with the parasite walked freelyaround the test area.

But that's not all.The parasite was found to bemore powerful than originally thought--even after researchers cured the mice ofthe infection.They no longer reacted with fear to a cat's smell,which couldindicate that the infection has caused a permanent change in mice's brains.

Why does a parasite change a mouse's brain insteadof making it sick like it does to humans?The answer lies inevolution."It's exciting scary to know how a parasite can manipulate amouse's brain this way,"Ingram said.But she also finds it inspiring."Typically if you have a bacterial infection,you go to a doctor and takeantibiotics and the infection is cleared and you expect all the symptoms toalso go away."She said,but this study has proven that wrong."Thismay have huge implications for infectious disease medicine."

Which of the following statements is trueaccording to the passage?查看材料

A.Toxoplasma gondii causes people strange anddeadly diseases
B.With certain infection the infectious diseasecannot be cured completely
C.Human beings infected by toxoplasma gondii willhave permanent brain damage
D.Toxoplasma gondii is harmful to human beings,butit does no harm to mice

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答案： B

本题解析：

细节题。寄生虫会对胎儿造成致命的伤害，故排除A；文章只表明这种感染对老鼠的大脑有永久性的改变，并没有提及人类，故排除c；寄生虫对人类有危害，但是并不能说明对老鼠没有危害，故排除D。最后一段指出，人们一旦受到细菌感染就希望服用抗生素来消除这种感染并希望所有的症状都能消失，但是这种想法是错误的，由此可以推断出B项是正确的。