final public function get_answers() {
        global $DB;
        if ($this->answers === null) {
            $this->answers = array();
            $answers = $DB->get_records('lesson_answers', array('pageid'=>$this->properties->id, 'lessonid'=>$this->lesson->id), 'id');
            if (!$answers) {
                // It is possible that a lesson upgraded from Moodle 1.9 still
                // contains questions without any answers [MDL-25632].
                // debugging(get_string('cannotfindanswer', 'lesson'));
                return array();
            }
            foreach ($answers as $answer) {
                $this->answers[count($this->answers)] = new lesson_page_answer($answer);
            }
        }
        return $this->answers;
    }