如何使用php中的单选按钮获取输入

I'm having a problem. Actually I'm making a quiz in php. So my client will be having 4 options which are displayed in radio buttons. So I want to get the option he/she has selected in the variable $ answer so how to do that. My code is as follows:

<?php

$qid = $_POST['q_id'];
$con = mysql_connect('localhost', 'root', '') or die(mysql_error());
$db  = mysql_select_db('quiz', $con) or die(mysql_error());
$q   = "select * from question where qno=$qid";
$rq  = mysql_query($q,$con);

echo $rq;

if(!$rq)
{
    echo " the sql query faiiled to work ";
}else
{
    while ($sub_row=mysql_fetch_array($rq))
    {
        $id=$sub_row["qno"];
        $question=$sub_row["question"];
        $option1=$sub_row["option1"];
        $option2=$sub_row["option2"];
        $option3=$sub_row["option3"];
        $option4=$sub_row["option4"];

        echo "<h5>Q".$id." : ".$question."</br></h5>";   
        echo "</br></br>";
        echo "<h4><input type= radio name=\"{$id}\" value=\"{$option1}\">$option1</h4></br>";
        echo "<h4><input type= radio name=\"{$id}\" value=\"{$option2}\">$option2</h4></br>";
        echo "<h4><input type= radio name=\"{$id}\" value=\"{$option3}\">$option3</h4></br>";
        echo "<h4><input type= radio name=\"{$id}\" value=\"{$option4}\">$option4</h4></br></br>";
    }
}

?>

You can add <input type='hidden' name='question' value='{$id}'>

And then it's easy - $answer = $_POST[$_POST['question']]