To allow operators from separate units to perform work routed to both units, the most effective solution is to associate each operator with the same work group. By doing this, all operators in the work group can share and manage tasks regardless of their specific unit, ensuring that any work routed to the work group can be handled by any of the operators. This contrasts with having to individually associate each operator with multiple units or with each unit associating multiple operators, which would be less efficient and scalable. Thus, the correct configuration is to associate the operators with the same work group.