Why are these errors occurring?

A company’s static website hosted on Amazon S3 was launched recently, and is being used by tens of thousands of users. Subsequently, website users are experiencing 503 service unavailable errors.

Why are these errors occurring?
A . The request rate to Amazon S3 is too high.
B . There is an error with the Amazon RDS database.
C . The requests to Amazon S3 do not have the proper permissions.
D . The users are in different geographical region and Amazon Route 53 is restricting access.

Answer: A