<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<!--Fig. J.1: main.html -->
<!--Our first Web page. -->
<html xmlns = "http:www.3.org/TR/1999/xhtml">
<head>
<title>Our first Web page<title>
</head>
<body>
<p>Welcome to XHTML!</P>
<body>
</html>
------解决方案--------------------
楼上正解