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请阅读Passage l。完成第21—25小题。

Passage 1

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

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

The parasite, called Toxoplasma gondii, might sound unfamiliar to you, but the shocking fact is that up to one-third of people around the world are infected by it. This parasite can cause different diseases among humans, especially pregnant women--it is linked to blindness and the death 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(尿) before and after it was infected by the parasite. They noted that normal mice stayed far away from the urine while mice that were infected with the parasite walked freely around the test area.

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

Why does a parasite change a mouse's brain instead of making it sick like it does to humans?

The answer lies in evolution.

"It's exciting scary to know how a parasite can manipulate a mouse'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 take antibiotics and the infection is cleared and you expect all the symptoms to also go away."

She said, but this study

A.Toxoplasma gondii causes people strange and deadly diseases
B.With certain infection the infectious disease cannot be cured completely
C.Human beings infected by toxoplasma gondii will have permanent brain damage
D.Toxoplasma gondii is harmful to human beings, but it does no harm to mice

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答案： B

本题解析：

寄生虫会对未出生的小孩造成致命性的伤害，故A排除；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C排除；寄生虫对人类有危害，但是并不能说明对老鼠没有危害，故D排除。文章最后一段指出．人们一旦受到细菌感染就希望吃抗生素来清除所有的感染并希望所有的症状都能消失．但是这种想法是错误的．也可以推断出B是正确的。