____________ is a fast, flexible, fully managed pub/sub messaging service?

Explanations:

Amazon SQS (Simple Queue Service) is a fully managed message queuing service, not a pub/sub service. It is used for decoupling distributed systems but does not support the publish-subscribe model.

Amazon SES (Simple Email Service) is a scalable email sending service, not a pub/sub messaging service. It is primarily used for sending transactional and marketing emails.

Amazon FPS (Flexible Payment Service) is a service used for managing online payments, not a pub/sub messaging service. It has been deprecated and replaced by Amazon Pay.

Amazon SNS (Simple Notification Service) is a fully managed pub/sub messaging service. It supports the publish-subscribe model, allowing messages to be sent to multiple subscribers.