The correct answer is D, Amazon GuardDuty. GuardDuty is a threat detection service designed to continuously monitor and protect AWS accounts and workloads. It uses machine learning, anomaly detection, and integrated threat intelligence to identify potential security issues such as unauthorized access, compromised instances, and data exfiltration. When suspicious activities are detected, GuardDuty generates security findings and provides actionable insights for remediation. Additionally, it can integrate with AWS Lambda to automate responses to security findings, allowing for immediate actions against threats. The other options do not meet the criteria specified in the question: AWS Trusted Advisor provides recommendations to help improve AWS account's security and performance, Amazon Detective uses graph theory to perform investigations of data security issues, and Amazon Inspector assesses applications for vulnerabilities or deviations from best practices, but neither of these services offer the continuous monitoring and automated threat response capabilities of GuardDuty.