我需要6个人的3个问题。但每次随机显示快4题。

/*for random question*/
public function qustionShow($question){

    $query = $this->conn->query("select * from question where cat_id='$question'");
    $c = mysqli_num_rows($query);
    $rand = rand(3, $c)-3;

    $show = $this->conn->query("select * from question where cat_id ='$question' and id >'$rand' LIMIT 3");
    while ($row=$show->fetch_array(MYSQLI_ASSOC)){
        $this->qus[]=$row;
    }
    return $this->qus;  
}