The correct answer is A because Workday allows administrators to keep a broad worker population in a single benefit group while restricting access to a specific plan through a Benefit Plan Eligibility Rule. In this case, all full-time employees belong to one benefit group, but only those with more than twenty years of service should be allowed to enroll in the medical plan. The correct design is to assign the plan to the existing benefit group and then attach a worker-based eligibility rule on the plan itself using the Worker Plan Eligibility field.

This approach avoids unnecessary creation of another benefit group and keeps the overall benefits structure simpler and easier to maintain. Option B is incorrect because manual communication and intervention are not proper configuration controls for eligibility. Option C is also incorrect because Provider ID is not intended to manage service-based plan eligibility. Option D is not appropriate because launching a separate enrollment just for one eligibility condition creates administrative complexity and does not solve the configuration requirement cleanly. Plan-level eligibility rules are the standard Workday method for handling this scenario.