The correct answer is D, AWS X-Ray. AWS X-Ray is a service that enables developers to analyze and debug production, distributed applications, including those built using a microservices architecture. It provides an end-to-end view of requests as they travel through the application, allowing developers to identify and troubleshoot performance issues and errors. X-Ray offers visibility into the underlying components of the application and helps trace requests as they flow through different AWS resources and services. This service is specifically designed for monitoring the performance of distributed applications, which is why option D is the correct choice.