public function get_total_mark() {
        $mark = 0;
        foreach ($this->questionattempts as $qa) {
            if ($qa->get_max_mark() > 0 && $qa->get_state() == question_state::$needsgrading) {
                return null;
            }
            $mark += $qa->get_mark();
        }
        return $mark;
    }