按照图片中所说，则运行结果只有两张图（一张被覆盖）但为什么实际不是这样的？
<html>
<head>
<style type = "text/css">
#a {
float : left;
}
img {
display:block;
}
</style>
</head>
<body>
<img id = "a" src="/i/eg_mouse.jpg" width="50" height="50">
<img id = "b" src="/i/eg_mouse.jpg" width="50" height="50">
<img id = "c" src="/i/eg_mouse.jpg" width=50" height="50">
<p>通过改变 img 标签的 "height" 和 "width" 属性的值，您可以放大或缩小图像。</p>
</body>
</html>
