不能访问函数中的变量


couldn't access variable in the function

我无法访问show_form()函数中的$connection变量。我得到未声明的变量错误。我要怎么做才能访问函数中的这个变量?

<html>
<body>
<?php
include('db.php');
$connection = mysqli_connect($db_host, $db_username, $db_password, $db_database);
    if (isset($_POST['submit-button'])){
        require_once 'process1.php';
        if($form_errors = validate_form())
        {
            show_form($form_errors);
        }
        else
        {
            process_1();
        }
    }
    else{
        show_form();
    }
?>
function show_form($errors = ''){
<form id='myForm'>
<?php
    echo "<SELECT id='test' >'n";
    echo "<option value=''></option>'n";
    if ($result = $connection->query("SELECT col1, col2 FROM table1 order by col1"))
    {
        while($row = $result->fetch_assoc()) 
        {
            echo "<option value='{$row['col1']}'>{$row['col2']}</option>'n"; 
        }
    }
    echo "</select>'n";
?>
</form>
<?php
}
?>
</body>
</html>

在调用此函数时传递$connection变量作为参数

<?php function show_form($errors = '',$connection){?>
    <form id='myForm'>
    <?php
                echo "<SELECT id='test' >'n";
                echo "<option value=''></option>'n";
                if ($result = $connection->query("SELECT col1, col2 FROM table1 order by col1"))
                {
                    while($row = $result->fetch_assoc()) 
                    {
                        echo "<option value='{$row['col1']}'>{$row['col2']}</option>'n"; 
                    }
                }
                echo "</select>'n";
            ?>
    </form>
    <?php
    }