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Galileo lived in the city of Pisa, where there is a leaning tower about 180 __1__ high.  From the top
__2__ the tower Galileo dropped a light ball and a heavy ball exactly at __3__ same time.  They __4__
fell at about the same speed and hit ground together.  He __5__ it again and again.  Every time he got the
same result.  At last, he decided __6__ he had found the truth about __7__ objects.  As we know now,
heavy objects and light objects fall at the same speed unless air holds __8__ back.  A feather falls
__9__ than a stone only because the air holds the feather back more than it __10__  the stone.

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