<html>
<head>
<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$(".intro,.demo,.end").css("background-color","yellow");
});
</script>
</head>
<body>
<h1>Welcome to My Homepage</h1>
<p class="intro">This paragraph has class "intro".</p>
<p>This is a paragraph.</p>
<p class="demo">This paragraph has class "demo".</p>
<p>This is another paragraph.</p>
<p class="end">This paragraph has class "end".</p>
</body>
</html>