阅读下列短文.根据所读内容在文章后的表格中填入恰当的单词(注意:表格中的每个空只填一个单词) For more than twenty years scient

阅读下列短文，根据所读内容在文章后的表格中填入恰当的单词（注意：表格中的每个空只填一个单词）

For more than twenty yearsscientists have been seeking to understand the mystery of the ‘‘sixthsense" of direction．By trying out ideas and solving problems one by one，they are now getting closer to one answer．

One funny idea is thatanimals might have a built-in compass(指南针)．

Our earth itself is a bigmagnet(磁体)．So a little magnetic needle that swings freely lines

itself with the big earth magnet topoint north When people discovered that idea about a thousand years ago andinvented the compass，it allowed sailors to navigate (航海)on ocean voyages,even under cloudy skies.

 Actually the idea ofthe living compass came just from observing animals in nature．

 Many birds migratetwice a year between their summer homes and winter homes．Some of them fly forthousands of kilometers and mostly at night．Experimentshave shown that some birds can recognize star patterns．Butthey can keep on course even under cloudy skies．How canthey do that?

A common bird that does notmigrate but is great at finding its way home is the homing pigeon．Not all pigeons canfind their way home．Those that can are very good at it，and they have been widely studied．

One interesting experimentwas to attach little magnets to the birds’ heads to block their magneticsense—just as a loud radio can keep you from hearing a call to dinner．On sunny days, thatdid not fool the pigeons．Evidently they can use the sunto 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 thesame kind of results were done with honeybees．These insects also seem to have aspecial sense of direction．

In spite of the experiments，the idea of an animalcompass seemed pretty extraordinary．How

would an animal get the magnetic stufffor a compass.

An answer came from anunexpected source．A scientist was studying bacteria that live in the

mud of ponds and marshes．He found accidentallylittle rod-like bacteria that all swam together inone direction—north．

Further study showed thateach little bacterium had a chain of dense particles inside，which

proved magnetic．The bacteria had madethemselves into little magnets that could line up with the

earth’s magnet．

The big news was that aliving thing，even a simple bacterium，can make magnetite．That led

to a search to see whether animals mighthave it.. By using a special instrument called magnetometer，scientists were ableto 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 compassbegan to seem reasonable．

试题答案

【答案】

 swinging

 Based

 migration

 even

 experiments／tests／study／research

 block

 cloudy

 discovery

 north

 brain(s)

【解析】

试题