为什么这样 right无法与mid和left并列
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<title>无标题文档</title>
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*{margin:0; padding:0;}
#wrap{width:970px; margin:0 auto;}
#mainbody{margin-top:15px;}
#left{float:left; width:110px; }
#mid{float:left; margin-left:123px; width:650px;border:1px solid #999; }
#right{float:right; border:1px solid red ; }
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<div id="header"><img src="http://img1.sycdn.imooc.com//5369cd6e0001a15b09700088.jpg" width="970" height="88" /></div>
<div id="mainbody">
<div id="left"><img src="http://img1.sycdn.imooc.com//5369cd0e00011e3901090487.jpg" width="109" height="487" /></div>
<div id="mid"><img src="http://img1.sycdn.imooc.com//5369cd3c00013e9e06490439.jpg" width="649" height="439" /></div>
<div id="right"><p>欢迎使用金山软件出品的爱词霸，在线查询你英语词汇、句子释义</p><img src="http://img1.sycdn.imooc.com//5369cd540001d8e101770329.jpg" width="100" height="329" /></div>
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