如图所示，两个固定的等量异种电荷，在它们连线的垂直平分线上有a、b、c 三点，则（   ）

     The children often play soccer in the garden(花园). Sometimes they break (打破).Mrs. Smith’s windows.  
One afternoon , Mrs. Smith is reading a newspaper at home. After a short time, she closes her eyes and goes to sleep. At that time a little boy knocks(敲) at the door. Mrs. Smith opens the door and asks, “Do you break my windows again（又一次）?” “Oh, no”, says the boy. “ Your windows are open this time and our soccer is in your room. Can I get it back, please?” 
根据短文内容，选择正确答案。

日常生活中人们常喝纯净水，市场出售的纯净水有一些是蒸馏水，对于这一类纯净水的说法，正确的是（　　）