怎么通过父容器，改变图像显示的大小，
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>图像</title>
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css">
</head>
<body>
<div class="container">
<div class="row">
<div class="col-sm-4">
<img alt="140x140" src="http://placehold.it/140x140">
<div>默认图片</div>
</div>
<div class="col-sm-4">
<img class="img-rounded" alt="140x140" src="http://placehold.it/140x140">
<div>圆角图片</div>
</div>
<div class="col-sm-4">
<img class="img-circle" alt="140x140" src="http://placehold.it/140x140">
<div>圆形图片</div>
</div>
<div class="row">
<div class="col-sm-6">
<img class="img-thumbnail" alt="140x140" src="http://placehold.it/140x140">
<div>缩略图</div>
</div>
<div class="col-sm-6" style="width: 1000px;height: 1000px;"> //我在这里都加了父容器的大小，但是感觉图像大小没变化啊？？？？
<img class="img-responsive" alt="140x140" src="http://placehold.it/140x140" />
<div>响应式图片</div>
</div>
</div>
</div>
</div>
</body>
</html>
