private function parenthesesMerge($parts)
    {
        $subsentences = [];

        foreach ($parts as $part) {
            if ($part[0] === ')') {
                $subsentences[count($subsentences) - 1] .= $part;
            } else {
                $subsentences[] = $part;
            }
        }

        return $subsentences;
    }