Which of the following is NOT a responsibility of a COR?

In the context of a Contracting Officer Representative (COR), the primary responsibilities include monitoring contractor performance, reviewing and approving invoices, and maintaining contract files. Negotiating subcontracts with suppliers falls outside the remit of a COR because this responsibility is typically reserved for contracting officers who have the authority to engage in such negotiations. The COR's role is more focused on oversight and administration rather than the contractual dealings with subcontractors, which requires a higher level of authority and expertise in contract negotiations.

Therefore, understanding the boundaries of a COR's role is crucial, as it helps clarify the distinctions between the duties of a COR and those of a contracting officer. This ensures that the COR effectively supports contract management without overstepping into areas that require different delegation of authority.