为什么这段代码输出 4 而其他所有内容都没有输出?
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>jQuery</title>
<script src="jquery-1.9.1.js"></script>
<script>
$(document).ready(function() {
var par = $("p");
document.write(par.length);
});
</script>
</head>
<body>
<p>I am one</p>
<p>I am two</p>
<p>I am three</p>
<p>I am four</p>
</body>
</html>