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Sir Isaac Newton was a scientist who discovered the law of gravity（重力）. People have learned that Isaac Newton once ______ when he was thinking under an apple tree. ______ he was woken up by an apple falling on his head. He jumped up, shouting, “Gravity made the apple fall!”

Did the apple really fall on him? No one ______ for sure. The story of the apple may have some ______, but people who knew him have written that it never happened. Newton had actually been studying gravity and thinking about how apples fell down from a tree and not ______ for many years.