public function subscriptions(array $options = [])
    {
        $resultLimit = $this->pluck('resultLimit', $options, false);

        return new ItemIterator(
            new PageIterator(
                function (array $subscription) {
                    return $this->subscriptionFactory(
                        $subscription['name'],
                        $subscription['topic'],
                        $subscription
                    );
                },
                [$this->connection, 'listSubscriptions'],
                $options + ['project' => $this->formatName('project', $this->projectId)],
                [
                    'itemsKey' => 'subscriptions',
                    'resultLimit' => $resultLimit
                ]
            )
        );
    }