How can I rewrite this code to improve its clarity?
<p>Could you write this 'cleaner' ? Just a simple question from a beginner:)</p>

<pre><code>if(isset($_GET['tid']) &amp;&amp; trim($_GET['tid'])!==""){
$act = 'tid';
$tid = trim($_GET['tid']);

}elseif(isset($_GET['fid']) &amp;&amp; trim($_GET['fid'])!==""){
$act = 'fid';
$fid = trim($_GET['fid']);

}elseif(isset($_GET['mid']) &amp;&amp; trim($_GET['mid'])!==""){
$act = 'mid';

}elseif(isset($_GET['act']) &amp;&amp; trim($_GET['act'])!==""){
$act = trim($_GET['act']);

}else{
$act = "";
}
</code></pre>
