Не опознает переменную

<?php
if(isset($_GET['b']))
{
$b = $_GET['b'];
$sql = new sql();
$result_query = $sql->selectionIdGroup();       
}
echo'
<ul class="filetree" id="menu">
<ul>
    <ul>
  <li class="closed"><span class="folder">ОАО ХК "Элинар"</span>
        <ul>
    <li><span class="file"><a href="branch.php?'.$b.'">Приемная</a></span></li>
        </ul>

public static function selectionIdGroup()
    {   
        $b = $_GET['b'];
        $sql = "SELECT `id_b`,`id_p`,`id_t`,`fam` FROM `users` WHERE b = $b";
        $query = mysql_query($sql) or die (mysql_error());
        $b = $_GET['b'];
        while($row = mysql_fetch_array($query))
        {
                $sqlTel = "SELECT `telephone` FROM `telephone` WHERE id_t='{$row['id_t']}'";
                $queryTel = mysql_query($sqlTel);
                $rowTel = mysql_fetch_array($queryTel);
                $sqlPost = "SELECT `post` FROM `post` WHERE id_p='{$row['id_p']}'";
                $queryPost = mysql_query($sqlPost);
                $rowPost = mysql_fetch_array($queryPost);
                $sqlBranch = "SELECT `branch` FROM `branch` WHERE id_b='{$row['id_b']}'";
                $queryBranch = mysql_query($sqlBranch);
                $rowBranch = mysql_fetch_array($queryBranch);
                echo '<table border=1 width=800px align=center cellpadding=0 cellspacing=0 bgcolor=#ccff99><tr><td width=200px>'.$row['fio'].'</td><td width=200px>'.$rowBranch['branch'].'</td><td width=200px>'.$rowPost['post'].'</td><td width=200px>'.$rowTel['telephone'].'</td></tr></table>';
 
        }
        
    }