herkese selamlar kolay gelsin arkadaşlar

çok aradım ama bulamadım bir yer yanışi ama göremedim sorun nerde aşşağıdaki gibi hata alıyorum

Fatal error: Uncaught Error: Call to undefined function execute() in C:\wamp64\www\dersler\dah.php on line 21
( ! ) Error: Call to undefined function execute() in C:\wamp64\www\dersler\dah.php on line 21




<?php 
try  {
	$veritabani = new PDO("mysql:host=localhost;dbname=stoktakip;charset=utf8", "root","123456");
	$veritabani->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
	
	
} catch (PDOException $e) {
	die($e->getMessege());
	
}




class stok {
	
	function katogoriust ($veritabani){
		
	$sorgu="select * from kategori ";
	$verson=$veritabani->prepare($sorgu);
	$verson=execute();
	
	while($sonson=$verson->fetch(PDO::FETCH_ASSOC)):
	?>
	<a id="link" href="#" style="padding-top:40px;"><?php echo $sonson["ad"]; ?></a>
	<?php
	
	endwhile;	
		
		
		}
	
	
	
	}

?>
index php

<?php  require_once("dah.php"); 
$stok= new stok;
try  {
	$veritabani = new PDO("mysql:host=localhost;dbname=stoktakip;charset=utf8", "root","123456");
	$veritabani->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
	
	
} catch (PDOException $e) {
	die($e->getMessege());
	
}

 ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>
<link rel="stylesheet" href="dosya/tasarim.css" />
<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>STOK TAKİP SİSTEMİ</title>
</head>
<body>

<div class="container table-bordered" id="cont">

<!-- ÜST BÖLÜM -->
<div class="row border-bottom" style="min-height:60px">
		<div class="col-md-3" id="ustbolum"><h4>Kullanıcı Adı</h4></div>
		<div class="col-md-9" id="ustbolum"><ul class="nav justify-content-end" >
  <li class="nav-item"  id="islem">
    <a class="nav-link btn btn-outline-dark" href="#">İşlemler</a>
  </li>
  <li class="nav-item" id="islem">
    <a class="nav-link btn btn-outline-dark" href="#">Şifre Değiştir</a>
  </li>
  <li class="nav-item" id="islem">
    <a class="nav-link btn btn-outline-dark"  href="#">Çıkış</a>
  </li>

</ul></div>
</div>
<!-- ÜST BÖLÜM -->

<!-- KATEGORİ BÖLÜM -->
<div class="row border-bottom">
<?php 
	$stok->katogoriust($veritabani);
	 ?>
</div>
		<div class="col-md-3"><form class="form-inline">
  <label class="my-1 mr-2" for="inlineFormCustomSelectPref">Listeleme</label>
  <select class="custom-select my-1 mr-sm-2" id="inlineFormCustomSelectPref">
    <option value="1">Kutu</option>
    <option value="2">Liste</option>
     </select>
  <button type="submit" class="btn btn-primary my-1">Uygula</button>
</form></div>
</div>
<!-- KATEGORİ BÖLÜM -->

<!-- ORTA BÖLÜM -->
<div class="row">



 <!-- LİSTELEME İSKELET

<table class="table table-hover text-center">
    <thead>
      <tr>
        <th>Ürün Adı</th>
        <th>Stok Durumu</th>
        <th>İşlem</th>
      </tr>
    </thead>
    
    <tbody>
    
      <tr>
        <td>Ürün Adı</td>
        <td><b class="text-danger">000</b></td>
        <td><input name="guncel" type="submit" class="btn btn-outline-success" value=">" style="margin-bottom:3px; " /></td>
      </tr>
   <!-- EKLEMELER BURADAN DEVAM EDECEK 
   
      
    </tbody>
  </table>
-->





<!-- KUTU LİSTENİN İSKELETİ

		<div class="col-md-1 table-bordered " id="kutuliste">        
        <div class="row" style="text-align:center">
        <div class="col-md-12" >Ürün Adı</div> 
          <div class="col-md-12"><b class="text-danger">Stok :</b></div> 
        <div class="col-md-12"><input name="guncel" type="submit" class="btn btn-outline-success" value=">" style="margin-bottom:3px; " /></div>        
        </div>
        
        </div>
        
 -->   
		
</div>
<!-- ORTA BÖLÜM -->






</div>

<div class="container table-bordered table-info text-center">
<!-- SAYFALAMA BÖLÜM -->
<div class="row" style="min-height:30px;">
		<div class="col-md-12">SAYFALAMA</div>		
</div>
<!-- SAYFALAMA BÖLÜM -->
</div>

</body>
</html>