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（迁徙）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（鹤子）and they have been widely studied．One interesting experiment was to attach little magnets （磁铁，磁场）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．answer 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 本文属于说明文，介绍了鸟儿等动物天生就有能力识别方向，主要是因为它们有内置的指南针，本文对这一现象进行了研究说明．
解答 DBAD
32．D 主旨大意题 根据第一段最后一句One funny idea from observing animals in nature is that animals might have a built-in compass．可知关于动物奇怪的方向感，人们发现可能是动物体内有一个内置的磁盘，接下来科学家就对这一观点通过实验进行证明，故D正确．
33．B 推理判断题 根据本段最后一句In fact，the bacteria had made themselves into little magnets that could line up with the earth's magnet．可知实际上地球本身就是一个大磁场，动物身上的磁性都是因为地球磁场而有的，故B正确
34．A 词义猜测题 根据本句Experiments have shown that some birds can recognize star patterns．But they can keep on course even under cloudy skies．可知一些鸟通过
识别星星的位置来寻找路径，但是在有乌云的晚上，无法看到星星，它们仍旧可以按照正确的路线飞行，所以keep on course意为A项内容
35．D 细节理解题 根据文章倒数第二段最后一句In each animal，except for the bee，the magnetic stuff was always in or close to the brain．可知鱼儿等动物的内置磁铁最可能存在于它们的大脑，故D正确．
点评 阅读理解题测试考生在阅读基础上的逻辑推理能力，要求考生根据文章所述事件的逻辑关系，对未说明的趋势或结局作出合理的推断；或根据作者所阐述的观点理论，对文章未涉及的现象、事例给以解释．考生首先要仔细阅读短文，完整了解信息，准确把握作者观点．
