Final answer:
Amazon RDS has encryption enabled by default to protect data, while Amazon S3, AWS Lambda, and Amazon EC2 offer encryption as an optional feature that can be enabled if desired.
Step-by-step explanation:
You've asked which of the following AWS services has encryption enabled by default. The answer is c) Amazon RDS. Amazon Relational Database Service (Amazon RDS) supports encryption at rest by default for all database instances launched using its default parameter group. This is done to secure your data and protect it from unauthorized access. However, other services such as Amazon S3, AWS Lambda, and Amazon EC2 do not have encryption enabled by default, but they do offer the option to enable encryption if desired.