题目内容：
根据以下内容回答题：Homing pigeons are placed in a training program from about the time they are twenty。Eight days of age．They are taught to enter the lon through a trap and to exercise above and around the loft．and graduaUy they are taken away for short distances in wicker baskets and released．They are then expected to find their way home in the shortest possible time．
In their training flights or in actual races，the birds are taken to prearranged distant point sand released to find their way back to their own logs．Once the birds are liberated，their owners，who are standing by at the home lofts，anxiously watch the sky for the return of their entries．Since time is of the essence，the speed with which the birds can be induced to enter the loft trap may make the difference between gaining a win or a second place．
The head of a homing pigeon is comparatively small，but its brain is one quarter large than that of the ordinary pigeon．The homing pigeon is very intelligent and will persevere to the point of stubbornness；some have been known to fly a hundred miles off course to avoid a storm．
Some homing pigeon experts claim that this bird is gifted with a form of built-in radar that helps it find its own loft ager hours of flight，for hidden under the head feathers are two very sensitive ears，while the sharp，prominent eyes can see great distances in daytime．
Why do homing pigeons fly homeg They are not unique in this inherent skill；it is found in most migratory birds，in bees，ants，toads，and even turtles，which have been known to travel hundreds of miles to return to their homes．But in the animal world，the homing pigeon can be trusted with its freedom and trained to carry out the missions that people demand．
What is the purpose of the passage? A．To convince the reader to buy a homing pigeon．
B．To inform the reader about homing pigeons and their training
C．To protect homing pigeons against the threat of extinction(绝迹)．
D．To encourage the owners of homing pigeons to set the birds free．
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