ตรวจคำตอบในการทำแบบฝึกหัดเพื่อจะคิดคะแนนค่ะ

<?php
/////////////////////////////////////////////////////////////////showQuestion.php/////////////////////////////////////////////////////////////////////
ob_start();
include "connect.php";
?>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">


<style type="text/css">
<!--
.style1 {
	font-family: Tahoma;
	font-size: 18px;
	color: #FFFFFF;
}
-->
</style>

<?
$ex_id = $_GET['ex_id'];
$sql = "select * from question where ex_id = '$ex_id' order by rand()";  //order by ques_id LIMIT 0,10"
$db_query = mysql_query($sql) or die("Select error");
$count = mysql_num_rows($db_query);
//$result = mysql_fetch_array($db_query);

if($count!=10)
{
	echo "<script>alert('ขออภัย ขณะนี้ยังไม่สามารถทำแบบทดสอบได้');history.back();</script>";
}
else 
{ ?>	

<form id="form1" name="form1" method="post" action="cal_score.php">
<table width="600">
	<tr bgcolor="#000099">
		<td><span class="style1"><center>แบบทดสอบบทที่ <? echo $ex_id ?></center></span></td>
	</tr>
	<tr>
		<td></td>
	</tr>
	<tr>
		<td></td>
	</tr>
	<tr>
		<td></td>
	</tr>
</table>
<?	$n=1;
	while ($r=mysql_fetch_array($db_query)) 
	{ 	
		$qid=$r[ques_id];
		$ques=$r[question];
		$c1=$r[choice1];
		$c2=$r[choice2];
		$c3=$r[choice3];
		$c4=$r[choice4];
		echo 
		"<table width='600'>
		<tr bgcolor='#B1C3D9'>
			<td><font class='font' size='3pt'><B>ข้อ $n. $ques </B></td>
		</tr>
		<tr>
			<td><INPUT TYPE='radio' NAME='select_$qid' VALUE='1'> $c1</td>
		</tr>
		<tr>
			<td><INPUT TYPE='radio' NAME='select_$qid' VALUE='2'> $c2 </td>
		</tr>
		<tr>
			<td><INPUT TYPE='radio' NAME='select_$qid' VALUE='3'> $c3 </td>
		</tr>
		<tr>
			<td><INPUT TYPE='radio' NAME='select_$qid' VALUE='4'> $c4 </td>
		</tr>
		</font>
		</table>
		<HR>";
		$n=$n+1;
	}
	?>
	<label>
  		<div align="center">
  		<input type="submit" name="Submit" value="ตรวจคำตอบ" />
  		</div>
  	</label>
</form>
<? }
mysql_close();
ob_end_flush();
?>