What should the solutions architect do to meet this requirement?

Explanations:

Amazon Inspector is a security assessment service that identifies vulnerabilities in EC2 instances and containers. It is not designed to protect against DDoS attacks on an ALB.

Amazon Macie is primarily focused on discovering and protecting sensitive data, such as personal information, rather than mitigating DDoS attacks.

AWS Shield Advanced provides enhanced DDoS protection for applications, including those behind an ALB. It can detect and mitigate DDoS attacks, offering the necessary security for the application.

Amazon GuardDuty is a threat detection service that monitors for malicious activity and unauthorized behavior, but it doesn’t actively prevent DDoS attacks. It is more for detection than mitigation.