public function mark_quiz_complete( $user_id, $course_id = null ) {
		$quizzes = learndash_get_course_quiz_list( $course_id, $user_id );
		if ( $quizzes ) {
			foreach ( $quizzes as $quiz ) {
				$this->quiz_list[ $quiz['post']->ID ] = 0;
			}
		}
		$quizz_progress = array();
		if ( ! empty( $this->quiz_list ) ) {
			$usermeta       = get_user_meta( $user_id, '_sfwd-quizzes', true );
			$quizz_progress = empty( $usermeta ) ? array() : $usermeta;
			foreach ( $this->quiz_list as $quiz_id => $quiz ) {
				$quiz_meta = get_post_meta( $quiz_id, '_sfwd-quiz', true );
				if ( learndash_is_quiz_complete( $user_id, $quiz_id, $course_id ) ) {
					continue;
				}
				$quizdata = array(
					'quiz'             => $quiz_id,
					'score'            => 0,
					'count'            => 0,
					'pass'             => true,
					'rank'             => '-',
					'time'             => time(),
					'pro_quizid'       => $quiz_meta['sfwd-quiz_quiz_pro'],
					'course'           => $course_id,
					'points'           => 0,
					'total_points'     => 0,
					'percentage'       => 100,
					'timespent'        => 0,
					'has_graded'       => false,
					'statistic_ref_id' => 0,
					'm_edit_by'        => 9999999,  // Manual Edit By ID.
					'm_edit_time'      => time(),          // Manual Edit timestamp.
				);
				$quizz_progress[] = $quizdata;
				if ( $quizdata['pass'] == true ) {
					$quizdata_pass = true;
				} else {
					$quizdata_pass = false;
				}
				// Then we add the quiz entry to the activity database.
				learndash_update_user_activity(
					array(
						'course_id'          => $course_id,
						'user_id'            => $user_id,
						'post_id'            => $quiz_id,
						'activity_type'      => 'quiz',
						'activity_action'    => 'insert',
						'activity_status'    => true,
						'activity_started'   => $quizdata['time'],
						'activity_completed' => $quizdata['time'],
						'activity_meta'      => $quizdata,
					)
				);
			}
		}
		if ( ! empty( $quizz_progress ) ) {
			update_user_meta( $user_id, '_sfwd-quizzes', $quizz_progress );
		}
	}