[...]中出现意外的“”

在课堂上，我在第22行收到“意外的''''[...]，而且我可以终生不知道为什么。

错误在第22行

<?php
namespace oowp\post;

global $wpdb;

class PostObjectQueryBuilder extends QueryBuilder implements IExtendable {
    use Extendable;

    // WP Tables
    private $tablePosts;             //The table of Posts.
    private $tablePostmeta;          //The Meta Content (a.k.a. Custom Fields) table.
    private $tableComments;          //The Comments table.
    private $tableCommentmeta;       //The table contains additional comment information.
    private $tableTerms;             //The terms table contains the 'description' of Categories, Link Categories, Tags.
    private $tableTermTaxonomy;      //The term_taxonomy table describes the various taxonomies (classes of terms). Categories, Link Categories, and Tags are taxonomies.
    private $tableTermRelationships; //The term relationships table contains link between the term and the object that uses that term, meaning this file point to each Category used for each Post.
    private $tableUsers;             //The table of Users.
    private $tableUsermeta;          //The usermeta table contains additional user information, such as nicknames, descriptions and permissions.
    private $tableLinks;             //The table of Links.
    private $tableOptions;           //The Options table.

    // LINE 22 BELOW
    const BASE_QUERY = "SELECT wp.ID FROM `{$this->tablePosts}` wp
        INNER JOIN `{$this->tablePostMeta}` wm ON (wm.`post_id` = wp.`ID`)
        INNER JOIN `{$this->tableTermRelationships}` wtr ON (wp.`ID` = wtr.`object_id`)
        INNER JOIN `{$this->tableTermTaxonomy}` wtt ON (wtr.`term_taxonomy_id` = wtt.`term_taxonomy_id`)
        INNER JOIN `{$this->tableTerms}` wt ON (wt.`term_id` = wtt.`term_id`)";

我尝试重写有问题的行，并尝试将const声明移到顶部，以及删除该use语句。两者都不起作用。