<form action='www.abcd.com/aboutus.php' method='get'>
 <select name="curr" id='test'>
 <option value="USD">USD</option>
 <option value="Euro">Euro</option>
 </select>
 <input type="submit" value="submit">
 </form>
on your pages simply put
 <? $curr = $_GET['curr'];  ?>
now on every link include
 abcd.com?curr=<? echo $curr ?>
9
solved Get url as www.abcd.com?curr=USD