Correct answer - "Cognito Sync" : Amazon Cognito Sync is an AWS service and client library that
enables cross-device syncing of application-related user data. You can use it to synchronize
user profile data across mobile devices and the web without requiring your own backend
Incorrect:
"Cognito Identity Pools" - Amazon Cognito identity pools provide temporary AWS credentials for
users who are guests
"S3" - S3 is a storage service that can be used from different devices however when you are
dealing with mobile app user data and syncing data Cognito Sync becomes a better solution as the
client libraries cache data locally so your app can read and write data regardless of device
connectivity status.
"EFS" - With Amazon EFS, you can create a file system, mount the file system on an Amazon EC2
instance, and then read and write data to and from your file system