php form submit

<form id="form1" name="form1" method="post" action="listproduct.php">  
按类别:<select size="1" name="p_category" id="p_category">
            <option value=""></option>
<?php
 $rs2=odbc_exec($conn,"select * from category");
if (!$rs2)
  {  echo "error";
     exit("Error in SQL");}
while (odbc_fetch_row($rs2))
{ $f = odbc_result($rs2,"categoryid");
  $h = odbc_result($rs2,"categorycn");
  $l = odbc_result($rs2,"categorycn");
echo '<option value="'.$f.'"> '.$f. ' '.$l.'</option>';
}
?>
</select>
<input type="submit" value="Submit" name="B1" class="input">  
</form>