Which AWS service meets these requirements?

Explanations:

AWS Shield is a managed DDoS protection service that safeguards applications from DDoS attacks but does not monitor for malicious activity or unauthorized behavior across AWS accounts or workloads.

AWS Firewall Manager is a security management service that allows you to centrally configure and manage firewall rules across multiple accounts but does not provide continuous monitoring for malicious activity or unauthorized behavior.

Amazon GuardDuty is a continuous threat detection service that monitors AWS accounts, workloads, and Amazon S3 buckets for malicious activity and unauthorized behavior. It analyzes data from AWS CloudTrail, VPC Flow Logs, and DNS logs to identify potential threats.

Amazon Inspector is an automated security assessment service that helps improve the security and compliance of applications deployed on AWS but does not provide continuous monitoring for malicious activity or unauthorized behavior.