任务型阅读
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．
