PHP - Enviar selected por get

$sql= "SELECT * FROM productos WHERE id =".$pid;

                $res2= mysql_query ($sql,$cnx);

                $modelo=mysql_fetch_array($res2);//obtengo el array de resultados

		echo '<select>';

			for ($i=1;$i<=$modelo['stock'];$i++){

                                 echo '<option value="'.$i.'" id="'.$i.'"> '.$i.'</option>';

			}

		echo '</select>';

				"</div>";

				echo '<div class="share-desc">

					<div class="share">

						<p>Share Product :</p>

						<ul>

					<li><a href="#"><img src="web/images/facebook.png" alt="" /></a></li>

					    	<li><a href="#"><img src="web/images/twitter.png" alt="" /></a></li>					    

			    		</ul>

					</div>';

					echo"<div class='button'><a href=carrito.php?pid=".$i.">Add to Cart</a></div>";

					echo $i;

<script>

   var scrt_var = 10;

   document.getElementById("link").setAttribute("href",scrt_var);

</script>

<a id="link">this is a link</a>

<script language="javascript" type="text/javascript">

var scrt_var = 10;

</script>

<a href="2.html" onclick="location.href=this.href+'?key='+scrt_var;return false;">Link</a>

echo '<option value="'.$i.'" id="'.$i.'"> '.$i.'</option>';

echo"<div class='button'><a href=carrito.php?pid=".$i.">Agregar a Carrito</a></div>";

<option value="7" id="7"> 7</option>

echo '<select id="stock">';

			for ($i=1;$i<=$modelo['stock'];$i++){

                                 echo '<option value="'.$i.'" id="'.$i.'"> '.$i.'</option>';

			}

		echo '</select>';

		echo"<div class='button'><a href='carrito.php' onclick=\"location.href=this.href+'?pid='+ObtenerValor();return false;\">Agregar a Carrito</a></div>";

?>

<script type="text/javascript">

	function ObtenerValor() {

		var valor = document.getElementById('stock').value;

		return valor;

	}

</script>