Final answer:
Both the Supervisory and Trainee Appraisers should have access to and retain a copy of the workfile, according to USPAP.
Step-by-step explanation:
According to USPAP (Uniform Standards of Professional Appraisal Practice), both the Supervisory Appraiser and the Trainee Appraiser have workfile obligations. It is NOT acceptable for the Supervisor to retain custody of the workfile and not allow the Trainee to access it (option B).
USPAP requires that both appraisers have access to and retain a copy of the workfile, either in physical or electronic format. This ensures transparency, accountability, and compliance with professional standards.