18．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 from observing animals in nature is that animals might have a built-in compass．
Many birds migrate（遷徙）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 horning pigeon（鶴子）and they have been widely studied．One interesting experiment was to attach little magnets （磁鐵，磁場）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．
In spite of the experiments，the idea of an animal compass seemed pretty extraordinary．How would animals get the magnetic stuff for a compass？An answer came from an unexpected source，A scientist was studying bacteria that lived in the mud of ponds．He found accidentally little rod-like bacteria that all swam together in one direction 一 north．In fact，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，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 close to the brain．
Thus，the idea of a built-in animal compass began to seem reasonable．
32．The main purpose of this passage is toD．
A．explain how the animal compass was invented
B．a(chǎn)nswer how an animal would get the magnetic stuff for a compass
C．introduce a famous experiment
D．prove the idea that animals might have a built-in compass
33．Which of the following can we infer from Paragraph 3？B
A．The bacteria magnetic sense seemed to be the same as the earth's．
B．The earth itself is a big magnet with which something magnetic might lines up
C．Little rod-like bacteria were found to swim north together through experiments．
D．Migrant birds can easily lose their way because of lacking magnetie．
34．The underlined words"keep on course"in the second paragraph means"A
A．stay in the correctflying route
B．lose one's way
C．remain calm
D．recognize star patterns
35．Where is probably the built-in magnet for a fish according to the scientists？D
A．Close to its stomach．
B．In its heart．
C．Far from its brain．
D．Inside its head．
分析 本文屬于說明文，介紹了鳥兒等動物天生就有能力識別方向，主要是因為它們有內(nèi)置的指南針，本文對這一現(xiàn)象進(jìn)行了研究說明．
解答 DBAD
32．D 主旨大意題 根據(jù)第一段最后一句One funny idea from observing animals in nature is that animals might have a built-in compass．可知關(guān)于動物奇怪的方向感，人們發(fā)現(xiàn)可能是動物體內(nèi)有一個內(nèi)置的磁盤，接下來科學(xué)家就對這一觀點通過實驗進(jìn)行證明，故D正確．
33．B 推理判斷題 根據(jù)本段最后一句In fact，the bacteria had made themselves into little magnets that could line up with the earth's magnet．可知實際上地球本身就是一個大磁場，動物身上的磁性都是因為地球磁場而有的，故B正確
34．A 詞義猜測題 根據(jù)本句Experiments have shown that some birds can recognize star patterns．But they can keep on course even under cloudy skies．可知一些鳥通過
識別星星的位置來尋找路徑，但是在有烏云的晚上，無法看到星星，它們?nèi)耘f可以按照正確的路線飛行，所以keep on course意為A項內(nèi)容
35．D 細(xì)節(jié)理解題 根據(jù)文章倒數(shù)第二段最后一句In each animal，except for the bee，the magnetic stuff was always in or close to the brain．可知魚兒等動物的內(nèi)置磁鐵最可能存在于它們的大腦，故D正確．
點評 閱讀理解題測試考生在閱讀基礎(chǔ)上的邏輯推理能力，要求考生根據(jù)文章所述事件的邏輯關(guān)系，對未說明的趨勢或結(jié)局作出合理的推斷；或根據(jù)作者所闡述的觀點理論，對文章未涉及的現(xiàn)象、事例給以解釋．考生首先要仔細(xì)閱讀短文，完整了解信息，準(zhǔn)確把握作者觀點．
