Which solution will meet these requirements?

Explanations:

Client-side encryption with customer-managed keys allows the application to encrypt data before it is sent to S3, ensuring that only the client holds the encryption keys. This method provides strong control over encryption but requires more management by the client.

Server-side encryption with AWS KMS keys (SSE-KMS) provides encryption at rest managed by AWS, but it does not satisfy the requirement of the company needing to encrypt the data before storing it, as the encryption is handled after the data reaches S3.

Server-side encryption with customer-provided keys (SSE-C) involves the client providing the keys for encryption and decryption, but AWS does not store the keys, which may lead to complications in managing sensitive data and could be less secure compared to client-side encryption.

Client-side encryption with Amazon S3 managed keys is not an option because S3 does not manage the keys for client-side encryption; it only manages server-side encryption. Therefore, this option does not meet the requirement of encrypting data before it is stored.