为什么第二个div不居中呢
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>对齐</title>
<style type="text/css">
#b{text-align:center;}
</style>
</head>
<body>
<div id=“a”><img src="http://img1.sycdn.imooc.com//52b4113500018cf102000200.jpg" ></div>
<div id=“b”><img src="http://img1.sycdn.imooc.com//52b4113500018cf102000200.jpg" ></div>
</body>
</html>
