private function pickTaskOptions(array $options)
    {
        // exclude task name.
        if (isset($options['args'])) {
            array_shift($options['args']);
        }

        // array to string.
        foreach ($options as $key => $value) {
            if ($key === 'args') continue;

            if ($key === 'option') {
                foreach ($value as $k => $v) {
                    $options[$k] = $v;
                }
                unset($options[$key]);
            } else {
                $options[$key] = array_pop($value);
            }
        }

        return $options;
    }