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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Perhaps you are located in China, where most people are prevented by the State Corporation, from accessing much of the Internet, including the on-line Encyclopaedia: Wikipedia.
Kind Regards....
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"The number of inventions increases faster than the need for them at the time" - SparkY
I certainly also knew in the Internet has very many resources,If may I also thought to search,but in fact I could not do,because this is our schoolwork,Please forgive.
All places that release pigeons at one time or the other loose some. A falcon has to eat. Storms along the way. People shooting at them for sport. There are other reasons that a homing pigeon due to injury will loose his way. Some just because the owners tax their systems too much.
Note if and when a pigeon recuperates from these injuries he at best stay lost.
People that rise homing pigeon do not keep the one's that are unreliable or tardy.
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Life is not a journey to the grave with the intention of arriving in a pretty, pristine body but rather to come sliding in sideways, all used up and exclaiming, "Wow, what a ride!"