AWS CloudFormation parameters allow templates to be reused across multiple environments by injecting environment-specific values at deployment time. AWS documentation recommends parameters for environment names such as dev, test, and prod.

To ensure unique resource names, CloudFormation intrinsic functions can dynamically construct names. Fn::Sub allows string interpolation, and !Ref retrieves the parameter value. Together, they enable resource names like myapp-dev-bucket or myapp-prod-role.

Conditions (Option B) control whether resources are created but do not generate unique names. Rules (Option C) validate parameters but do not affect naming. Fn::GetAtt (Option E) retrieves resource attributes and is not used to build names.

Therefore, defining an environment name parameter and using Fn::Sub with !Ref is the correct and AWS-recommended approach.