According to the PMBOK® Guide (6th Edition), the Estimate Activity Resources process is the process of estimating the team resources and the type and quantities of materials, equipment, and supplies necessary to perform project work.

Parametric Estimation is a specific Tool and Technique used in this process. It involves using an algorithm or a statistical relationship between historical data and other variables (e.g., square footage in construction, lines of code in software development) to calculate resource quantities.

Why Parametric Estimation is used here:

Scalability: If you know it takes one technician 2 hours to install one workstation, you can use that parameter to estimate the resources needed for 100 workstations.

Accuracy: When based on high-quality historical data, it provides a more accurate resource requirement than simple analogies.

Analysis of Distractors:

A (Plan Resource Management): This process is focused on establishing the approach and physical resource management strategies (the " how-to " document). It uses expert judgment and meetings rather than mathematical resource modeling like parametric estimation.

C (Estimate Costs): While Estimate Costs does use parametric estimation, the question specifically asks which process the project manager is developing within Project Resource Management. Estimate Costs belongs to the Project Cost Management knowledge area.

D (Acquire Resources): This is an executing process focused on obtaining the team members, facilities, equipment, and materials. The estimation should have been completed prior to this stage; here, the project manager uses negotiation, pre-assignment, and virtual team tools.