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        <title>菜鸟教程(runoob.com)</title> 
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            <h2>图片</h2>
            <p> .img-responsive类让图片支持响应式,将很好地扩展到父元素 (通过改变窗口大小查看效果):</p>                  
            <img src="tu/cat.jpg" class="img-responsive" alt="Cinque Terre" width="304" height="236"> 
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