Dúvida em enviar SELECT

<?
$username="root";
$password="";

if($link = new PDO('mysql:host=localhost;dbname=pesquisas', $username, $password)){
    echo "ok";
};

$query = "SELECT * from senso")
$result = mysqli_query($query);
$fetch = mysqli_fetch_row($result);
echo "$fetch[0]";