How can the user decrypt it?

A user has enabled serverside encryption with S3. The user downloads the encrypted object from S3. How can the user
decrypt it?

A.
S3 does not support server side encryption

B.
S3 provides a server side key to decrypt the object

C.
The user needs to decrypt the object using their own private key

D.
S3 manages encryption and decryption automatically

Explanation:
If the user is using the server-side encryption feature, Amazon S3 encrypts the object data before saving it on disks in its
data centres and decrypts it when the user downloads the objects. Thus, the user is free from the tasks of managing
encryption, encryption keys, and related tools.

http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingEncryption.html