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Exercising for 30 minutes a day is good for your health, a new Canadian study has found.  The study looked at 130,000 people in 17 countries.  Only 3% of the people did 30 minutes of a sport a day, like running or swimming.  But the researchers found that you don't need to do a sport or go to the gym---any form of physical activity is good for you, including housework.  Activities like cleaning are really good exercise, so you can stay healthy and have a clean house (             ).