【addclass】
<html>
<head>
<script type="text/javascript" src='http://code.jquery.com/jquery-1.5.2.js'></script>
<script type="text/javascript">
$(document).ready(function(){
$("p:last").addClass("selected");
});
</script>
<style>
.selected { color:red; }
</style>
</head>
<body>
<p>A</p>
<p>B</p>
<p>C</p>
</body>
</html>
