The correct service to mitigate Distributed Denial of Service attacks is AWS Shield. It provides automatic protection that safeguards web applications without necessitating any modifications to the existing setup. AWS Shield Standard is automatically included with certain AWS services such as Amazon CloudFront and provides protection against the most common attacks at no additional cost. For higher levels of protection, AWS Shield Advanced offers more comprehensive defenses against larger and more complex attacks, including access to the 24/7 AWS DDoS Response Team. AWS WAF primarily protects web applications from common web exploits that could affect application availability, security, and compliance, but is not directly aimed at DDoS protection. AWS Firewall Manager is a service that allows you to centrally manage firewall rules across your accounts and applications in AWS Organizations, but it does not directly mitigate DDoS attacks. Amazon Inspector is used to perform security assessments and find vulnerabilities, not for real-time attack mitigation.