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    One of the easiest ways to keep fit is to do jogging. Jogging is the name for a very gentle(舒缓的) running-it is just a little faster than walking.

    Start slow joging 20 meters , then walk 20 meters. Little by little , if you are not feeling very tired , you may do more jogging and less walking . Finally , jog the whole way . It will be easy for you to start jogging for 15 minutes twice a week , slowly, increase this to 20—30 minutes every day .The longer you join in jogging , the more you enjoy it and the healthier you will become . Some people like jogging alone , and others enjoy doing it with friends . Jogging in groups makes more people keener(热心的)，because you just can not stay in bed while there is a group of friends waiting outside.

    If you want to start jogging , prepare a pair of comfortable shoes and a determined mind.

猜谜语。

大丈夫不得出头。

谜底：____

材料二：李嘉图发展了斯密的国际分工理论,提出了比较成本学说,认为贸易的好处不是来自绝对优势,而是来自比较优势。