chekkbox怎么实现单独选项？或者直选2个不选3个，
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>form中的lable标签</title>
</head>
<body>
<form>
你对什么运动感兴趣：<br />
<label for="jog">慢跑</label>
<input type="checkbox" name="jog" id="jog" selected="selected" />
<br />
<label for="climbers">登山</label>
<input type="checkbox" name="climbers" id="climbers"/>
<br />
<label for="basketball">篮球</label>
<input type="checkbox" name="basketball" id="basketball"/>
</form>
</body>
</html>
