阅读下面短文，用方框内所给词汇的适当形式填空，使短文语义完整。
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The Ant and the Dove (鸽子)
One hot day, an ant was ____ for some water. After walking around ____ some time, she came to a river. To get to the river, she had to climb up a piece of grass.____ the ant was making her way up, she fell into the water.
Just then a dove up a ____ tree saw her. When the dove saw that the ant was in trouble, he ____ picked off a leaf and dropped ____ into the water near the ant. The ant moved towards the leaf____ climbed up there. Soon it carried her safely to dry ground. Just at that time, a hunter (猎人) nearby was going to shoot the dove. As soon as the ant found ____ the hunter was going to do, she quickly bit (咬)____ on the heel. Feeling the pain, the hunter ____ his gun. The dove was quick to fly away to safety.
上或圆内的任意一点，O为坐标原点，
，则
的最小值为（ ）
