xampp web server ทำระบบสุ่มข้อสอบ แล้วพบปัญหาเกี่ยวกับเรื่องของตัวแปรครับ

<?php 
		require "mysql.php";
		$sql = new mysql();	
		require "connection.php"; 
		
		$sql = "SELECT * FROM item_bank order by rand() limit 50";
		$run = mysql_query($sql);
		
		$i=0;
		
		while($data = mysql_fetch_array($run))
		{
			$i++;
			
			$item_no = $data['Item_No'];
			$question = $data['Question'];
			$choice1 = $data['Choice_A'];
			$choice2 = $data['Choice_B'];
			$choice3 = $data['Choice_C'];
			$choice4 = $data['Choice_D'];
			$answer = $data['Answer'];
			
			$arr = array($choice1,$choice2,$choice3,$choice4);
			shuffle($arr);
			
			if($arr[0]==$choice1){$a=1;}
			if($arr[0]==$choice2){$a=2;}
			if($arr[0]==$choice3){$a=3;}
			if($arr[0]==$choice4){$a=4;}
			
			if($arr[1]==$choice1){$b=1;}
			if($arr[1]==$choice2){$b=2;}
			if($arr[1]==$choice3){$b=3;}
			if($arr[1]==$choice4){$b=4;}

			if($arr[2]==$choice1){$c=1;}
			if($arr[2]==$choice2){$c=2;}
			if($arr[2]==$choice3){$c=3;}
			if($arr[2]==$choice4){$c=4;}

			if($arr[3]==$choice1){$d=1;}
			if($arr[3]==$choice2){$d=2;}
			if($arr[3]==$choice3){$d=3;}
			if($arr[3]==$choice4){$d=4;}
			
			echo "	<form name='form1' method='post' action='{$_SERVER['PHP_SELF']}'>";
			echo "	
					<table width='800px' border='0' align='center' cellspacing ='1'>
					
					<tr>
						<td colspan='2' align='left'>
							<input name=no$i type='hidden' value=$item_no>
							$i)  $question
						</td>
					</tr>
					</br>
					<tr>
						<td width='50%'> 
							<input name=c$i type='radio' value=$a checked>
							$arr[0]
						</td>

						<td width='50%'> 
							<input type='radio' name=c$i value=$b>
							$arr[1]
						</td>
					</tr>
					
					<tr>
						<td width='50%'> 
							<input type='radio' name=c$i value=$c>
							$arr[2]
						</td>
					
						<td width='50%'> 
							<input type='radio' name=c$i value=$d>
							$arr[3]
							<input name= answer$i type='hidden' value=$answer>
						</td>
					</tr>
					</table>
					</br>
					";
		}
			echo	"
					<div align='center'>
						<input type='hidden' name='line' value='$i'>
						<input type='submit' name='Submit' value='Submit'>
					</div>
					</form>
					";
		
	?>
     
        <?php
                
        if(isset($_POST['Submit']))
        {
			$score=0;
	
			for($i=1;$i<=$_POST['line'];$i++)
			{
				
				if($_POST['c$i'] == $_POST['answer$i'])
				{
					$score=$score+1;
				}
			}
	
			echo "Score : $score";
		}
	?>