找出圆与球的相似性质，并用圆的下列性质类比球的性质：
（1）圆心与弦（非直径）的中点的连线垂直于弦；
（2）与圆心距离相等的两弦相等；
（3）圆的周长C=πd（d是直径）；
（4）圆的面积S=πr2。
解：圆与球有下列性质类似：
圆是平面内到一定点的距离等于定长的所有点构成的集合，球面是空间中到一定点的距离等于定长的所有点构成的集合；圆是平面内封闭的曲线所围成的对称图形；球是空间中封闭的曲面所围成的对称图形，通过与圆的有关性质类比，可推测球的有关性质：
（1）球心与截面圆（不经过球心的小截面圆）的圆心的连线 垂直于截面；
（2）与球心距离相等的两个截面圆的面积相等；
（3）球的表面积S=πd2（d是直径）；
（4）球的体积
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| Last year, I learned from a newspaper that some sick kids needed help. I phoned the newspaper and I was asked to 1 a little girl named Lisa, who had mental illness. A short time later, I went for a 2 to Lisa. After having been at the mental hospital for years, she had recently been allowed to be at home. In the beginning, I did most of the 3 . Lisa, however, was too quiet and introverted (内向的), shyly sitting in the corner of the sofa and listening. She was careful not to allow our eyes to 4 .Over time, Lisa felt more comfortable little by little while I was 5 . Our weekly get-togethers usually 6 sharing a cup of hot coffee, window shopping or taking slow walks in the country. Lisa 7 discussed how she felt about our friendship, even after we completed our first year together. However, she knew she could always 8 me. Then one day I got a call from our volunteer group. "Mary, would you and Lisa like to be interviewed on a local TV news show?" Excited, I answered, "Wow! Let me discuss it with Lisa." I didn't think Lisa would be 9 going on "live" television. But to my surprise, Lisa wanted to be interviewed, too. At the interview, she said, " 10 I can help other people understand how important our 11 is, and how it has helped me, maybe they'll volunteer, too. Mary, wouldn't that be great?" With tears running down, we smiled at one another. From then on, Lisa never 12 a chance to plant seeds (种子) about the volunteer group with others. Her face lit up whenever she talked about our special fendship. | ||||
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