Which AWS service is always free of charge for users?
Amazon S3
Amazon Aurora
Amazon EC2
AWS Identity and Access Management (IAM)
Explanations:
Amazon S3 offers a free tier for the first 12 months, but usage beyond the limits incurs charges. It is not always free of charge.
Amazon Aurora has a free tier for the first 12 months, but it charges based on the usage of resources and storage after that.
Amazon EC2 provides a free tier for the first 12 months with limited usage, but beyond that, users will incur charges based on instance hours and usage.
AWS Identity and Access Management (IAM) is always free of charge. It allows users to manage access to AWS services and resources without any fees.
I deduce that the answer is:
AWS Identity and Access Management (IAM)