代码：
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<!--<meta http-equiv="x-ua-compatible" content="IE=edge">-->
<meta name="viewport" content="width=device-width,inital-scale=1">
<title>gird</title>
<link href="bootstrap-theme.min.css" rel="stylesheet">
</head>
<body>
<div class="container">
<div class="row">
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
<div class="col-md-1">.col-md-1</div>
</div>
</div>
</body>
</html>
为什么实现效果是竖着排列
