The correct answer is C, AWS Shield. AWS Shield is a managed service specifically designed to protect applications running on AWS from DDoS attacks. It provides automatic protection for all AWS customers at no additional cost through AWS Shield Standard. For more sophisticated and larger attacks, AWS Shield Advanced offers additional protections. The other options are incorrect because Amazon GuardDuty is an intelligent threat detection service, AWS WAF (Web Application Firewall) helps protect applications against common web exploits, and Amazon Inspector is an automated security assessment service for AWS applications.