Which AWS service should the administrator use to address these concerns?

Explanations:

AWS WAF (Web Application Firewall) is specifically designed to protect web applications from common threats like SQL injection and cross-site scripting (XSS) by allowing administrators to create rules that filter and monitor HTTP requests.

Amazon VPC (Virtual Private Cloud) is a service that enables the creation of isolated networks within AWS but does not provide specific protection against application-level threats like SQL injection or XSS.

Amazon GuardDuty is a threat detection service that monitors AWS accounts and workloads for malicious activity but does not specifically address web application security concerns such as SQL injection and XSS.

Amazon CloudWatch is primarily used for monitoring and logging AWS resources and applications; it does not provide direct protection against SQL injection or XSS attacks.