An organization is performing a vulnerability assessment for mitigating threats. James, a pen tester, scanned the organization by building an inventory of the protocols found on the organization's machines to detect which ports are attached to services such as an email server, a web server, or a database server.
After identifying the services, he selected the vulnerabilities on each machine and started executing only the relevant tests.
What is the type of vulnerability assessment solution that James employed in the above scenario?

A. Service-based solutions
B. Product-based solutions
C. Tree-based assessment
D. Inference-based assessment