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Old Smith is very fat. He always tells his son Little Smith that he wants to be thin. But Old Smith never does any exercise. He often eats hamburgers and meat. Sometimes he watches TV and eats ice cream all day long. And he gets up at 10 o'clock every day. One day, Little Smith asks Old Smith, "Why do you never do any exercise? You will always be so fat." Old Smith answers, "Why? I do sit-ups (仰卧起坐) every morning and every night! Every morning I get  'up' and every night I lie 'down'. "