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　　 Jeff Keith has only one leg. When he was 12 years old, Jeff had cancer. Doctors had to cut off most of his right leg.

       Every day Jeff puts on an artificial leg. With the plastic artificial leg, Jeff can ride a bicycle, swim, and play soccer. He can also run.

Jeff made a plan with his friends who had plastic legs, too. They decided to run across America.

      When he was 22 years old, Jeff Keith ran across the United States from the east to the west. He started running in Boston. Seven months later, he stopped running in Los Angeles. He ran 3, 200 miles. Jeff stopped in cities on the way to Los Angeles. In every city people gave Jeff money. The money was not for Jeff, but for the American Cancer Society.

        Jeff is disabled, but he can do many things. He is studying to be a lawyer. Jeff says, “People can do anything they want to do. I want people to know that I ran not only for disabled people, I ran for everybody. ”

下表是几种常用燃料（1mol）完全燃烧时放出的热量：