用PHP从选择下拉菜单中保存SQL变量

我有以下选择在我的代码。现在它将整个值发送到下一页，但是我如何将变量$dagen传递到下一页呢?

<form method="post" action="pagina4.php?lang=<?=$_SESSION['lang'];?>&naam=<?=$naam;?>&fietskeuze=<?=$fietskeuze;?>&opties=<?=$opties;?>&optieid=<?=$optieid;?>">
        <select id="dagen" name="dagen" style="width:250px;" style="height:250px;">
            <?php
            $query="SELECT * FROM $tabel WHERE fietstype='$fietskeuze'";
            $result=mysql_query($query) or die ("Ophalen prijzen mislukt: ".mysql_error());
            while ($row=mysql_fetch_array($result)) {
            $dagen=$row[dagen];
            $prijs=$row[prijs];
                echo "<option>
                    $dagen ".$lang['pagina3_dag']." - Tarief: EUR   ".$prijs."  
                </option>";
            }