新人学习PHP有关问题，发现书上代码不对

<br />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><br />
<?php<br />
	class Person<br />
	{<br />
		private $name;<br />
		private $sex;<br />
		private $age;<br />
		<br />
		function __construct($name="",$sex="男",$age=23)<br />
		{<br />
			$this->name=$name;<br />
			$this->sex=$sex;<br />
			$this->age=$age;<br />
		}<br />
		function say()<br />
		{<br />
			echo "我的名字  ".$this->name."，性别  ".$this->sex."，年龄  ".$this->age."<br>";<br />
		}<br />
		function run()<br />
		{<br />
			echo $this->name."正在走路<br>";<br />
		}<br />
	}<br />
<br />
	class Student extends Person <br />
	{<br />
		var $school;<br />
		function study()<br />
		{<br />
			echo $this->name."正在".$this->school."学习<br>";<br />
		}<br />
	}<br />
	class Teacher extends Student <br />
	{<br />
		var $wage;<br />
		function teaching()<br />
		{<br />
			echo  $this->sex."正在".$this->school."教学，每个月工资为".$this->wage."<br>";<br />
		}<br />
	}<br />
	$teacher1=new Teacher("张三","男",40);<br />
	$teacher1->school="沈阳工学院";<br />
	$teacher1->wage=3000;<br />
	<br />
	$teacher1->say();<br />
	$teacher1->run();<br />
	$teacher1->teaching();<br />
?><br />