<form action="ara.php" method="get">
<select name="select">
<option value="A RH +">A RH +</option>
</select>
<input type="submit" name="Submit" value="get">

<?php
include "baglan.php";
$veri = $_GET["select"];

$ara = mysql_query("select * from kisiler where kan = $veri");

while($bul = mysql_fetch_array($ara))
{
echo '$bul[Ad]';
echo '$bul[Soyad]';
}
?>