The correct answer is A, AWS Security Hub. It is a cloud security posture management service that automates security best practice checks, aggregates security alerts from various AWS services and third-party tools into a single, standardized format, and enables automated remediation. This service helps users to understand and improve their overall security posture across all of their AWS accounts. The other options, while related to security or optimization in some way, do not specifically provide the cloud security posture management functionality described in the question.