题目内容
Honeybees are disappearing for unknown reasons around the United States．Last winter, bees disappeared from 23 percent of American beekeeping businesses．Causes of the phenomenon, however, have remained a mystery．
Now, scientists from several universities and the United States Department of Agriculture say they have a possible explanation for the bee decline（数量下降）．It is a little known virus called Israeli acute--paralysis virus （IAPV） ．The virus kills bees．Researchers in Israel first described it in 2004 , but until now, bee experts hadn’t paid much attention to it．
When trying to find out why the bees were disappearing, a research team at Columbia University studied bee colonies （ 群体）, some with and the others without decline．The research turned up large numbers of two types of fungi （真菌） once suspected of causing the bee decline．The research results, however, showed that the fungi were almost as common in colonies without a decline as they were in colonies with a decline．The researchers concluded that the two fungi probably weren’t the cause．
Studies of the presence of IAPV, however, showed more interesting information．In those studies, done by a team at Pennsylvania State University in University Park, the virus showed up in 83 percent of samples from colonies with symptoms （症状）．Only five percent of samples from symptomless colonies had it．
Scientists still don’t know whether IAPIV can single--handedly cause the bee decline．They believe that even if the virus is making colonies sick , it could have a partner in crime．It’s possible, for instance, that insects or chemicals in the environment weaken bees, making them more likely to catch IAPV．
Scientists are still trying to figure out how IAPV came to the United States．The United States currently allows bee products to be imported from Canada, Australia, and New Zealand．If it turns out that this trade is spreading disease, the rules might eventually change．
According to the passage ，IAPV is a virus that ______．
A．hasn’t attracted much attention
B．well-known to doctors and scientist
C．was first found by Austrian researchers
D．is dangerous to animals and human beings
The underlined sentence in the fifth paragraph probably means______．
A．the virus could also cause other damages
B．there must be something that is the real cause
C．IAPV is not the only cause for the bee decline
D．the virus may be caused by the polluted environment
From the third and fourth paragraphs, we know researchers draw their conclusions by means of _______．
A．calculating B．comparing C．examining D．investigating
What still remains unknown to American scientists according to the passage?
A．How and why to kill IAPV．
B．How IAPV came to America．
C．Whether bee products should be imported．
D．How to change the rules of the bee products trade．
The best title for this passage would be _____．
A．Bee Disease B．How to Kill IAPV
C．A Virus—IAPV D．Two Types of Fungi
【小题1】A
【小题2】C
【小题3】B
【小题4】B
【小题5】A
解析:
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For more than twenty years scientists have been seeking to understand the mystery of the‘‘sixth sense"of direction．By trying out ideas and solving problems one by one，they are now getting closer to one answer．
One funny idea is that animals might have a built-in compass(指南针)．
Our earth itself is a big magnet(磁体)．So a little magnetic needle that swings freely lines
itself with the big earth magnet to point north and south．When people discovered that idea about athousand years ago and invented the compass，it allowed sailors to navigate (航海)on oceanvoyages, even under
cloudy skies.
Actuallly the idea of the living compass came just from observing animals in nature．
Many birds migrate twice a year between their summer homes and winter homes．Some of them fly for thousands of kilometers and mostly at night．Experiments have shown that some birds can recognize star patterns．But they can keep on course even under cloudy skies．How can they do that?
A common bird that does not migrate but is great at finding its way home is the homing pigeon．Not all pigeons can find their way home．Those that can are very good at it，and they have been widely studied．
One interesting experiment was to attach little magnets to the birds’ heads to block their
magnetic sense—just as a loud radio can keep you from hearing a call to dinner．On sunny days, that did not fool the pigeons．Evidently they can use the sun to tell which way they are going．But on cloudy days，the pigeons with magnets could not find their way．It was as if the magnets had blocked their magnetic sense．
Similar experiments with the same kind of results were done with honeybees．These insects also seem to have a special sense ot direction．
In spite of the experiments，the idea of an animal compass seemed pretty extraordinary．How
would an animal get the magnetic stuff for a compass.
An answer came from an unexpected source．A scientist was studying bacteria that live in the
mud of ponds and marshes．He found accidentally little rod-like bacteria that all swam together in
one direction—north．
Further study showed that each little bacterium had a chain of dense particles inside，which
proved magnetic．The bacteria had made themselves into little magnets that could line up with the
earth’s magnet．
The big news was that a living thing，even a simple bacterium，can make magnetite．That led
to a search to see whether animals might have it.. By using a special instrument called magnetometer，scientists were able to find magnetite in bees and birds，and even in fish．In each
animal，except for the bee．the magnetic stuff was always in or closer to the brain．
Thus．the idea of a built—in animal compass began to seem reasonable．
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The Magnetic Sense— The Living Compass |
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Passage outline |
Supporting details |
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The existence of the earth magnet and the invention of the navigating compass |
◇Our earth is a big magnet and a little freely (71) ▲ magnetic needle lines itself with the earth magnet to point north and south. ◇(72) ▲ on the idea above, the navigating compass was invented. |
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The possibility of birds’ built-in compasses |
◇ One piece of evidence is the (73) ▲ of many birds between their summer homes and winter homes. ◇ Birds can recognize star patterns on clear nights and keep on course (74) ▲ under cloudy skies |
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The (75) ▲ on pigeons’ and bees’ built-in compasses
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◇Little magnets were tied to the pigeons’ heads to (76) ▲ their magnetic sense. ◇The pigeons’ magnetic sense seemed to be affected on (77) ▲ days. ◇Similar things with the same results were done with bees. |
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The (78) ▲ of the magnetic stuff for the animal compass |
◇Little rod-like bacteria were found by chance to swim together in the direction of (79) ▲ . ◇Some animals had a chain of dense magnetic particles in or close to the (80) ▲ inside their bodies. |