我正在调用一个类，通过构造函数方法连接到我的本地mysql数据库。我得到一个500错误，当我启动php文件。我做错什么了吗？当我示例化这个类但无法连接时，我会将宿主用户pass和dbname的值传递到这个类中。db工作正常，因为我已经测试过了。

<?php

Class MyDB{

    public $query;
    public $myConnection;

    public function__construct($host, $username, $password, $dbname){

        $this->myConnection = mysqli_connect($host, $username, $password, $dbname);

    }

    public function listScores(){

        $this->query = "SELECT answer FROM correct_guesses" or die("error ..." . mysqli_error($this->$myConnection));

        $result = $this->$myConnection->query($this->query);

        while($row = mysqli_fetch_array($result)) {
        echo $row["answer"] . "<br>";

        }
    }
}

$score = new MyDB('localhost','root','root','scoreDB');

$score->listScores();

?>