找出这串代码的错误并给出正确答案<?php include_once "page.php"; class FirstPage extends Page { public function __construct($title) { parent::__construct($title); } public function DisplayContent() { ?> <form action="vote.php" method="post"> <table> <tr> <td>用户名:</td> <td><input type="text" name="username"></td> </tr> <tr> <td colspan="2"><button type="submit">下一步</button></td> </tr> </table> </form> <?php } } $page=new FirstPage("输入用户名"); $page->Display(); ?>

在代码的最后一行，`$page->Display()`应该改为`$page->DisplayContent()`，因为在FirstPage类中没有名为Display()的方法，只有DisplayContent()方法。修改后的代码如下：

<?php 
include_once "page.php"; 

class FirstPage extends Page { 
    public function __construct($title) { 
        parent::__construct($title); 
    } 

    public function DisplayContent() { 
        ?> 
        <form action="vote.php" method="post"> 
            <table> 
                <tr> 
                    <td>用户名:</td> 
                    <td><input type="text" name="username"></td> 
                </tr> 
                <tr> 
                    <td colspan="2"><button type="submit">下一步</button></td> 
                </tr> 
            </table> 
        </form> 
        <?php 
    } 
} 

$page = new FirstPage("输入用户名"); 
$page->DisplayContent(); 
?>