一个页面的图片多就容易造成加载慢，一个是需要整合图片到一起，减少图片大小及减少http请示次数。另一个就是使用懒加载来实现性能的提升，当滚动到一定高度的时候就预加载将要出现的图片。将页面内未出现在可视区域内的图片先不做加载， 等到滚动到可视区域后再去加载

<div class="t-b" data-src="/home/qiyefuwu/images/exam-13.jpg">
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