All three roles and responsibilities of financial intermediaries in a swap agreement are accurately defined. Financial intermediaries play a crucial role in swap agreements. They ensure that the obligations of the swap agreements are honored, even if the counterparty defaults. This is a significant role as it provides a safety net for the parties involved in the swap agreement. Secondly, financial intermediaries can enter into two offsetting transactions in a swap agreement without the knowledge of the two parties involved. This is possible because financial intermediaries have a broad network and can find parties willing to enter into swap agreements on similar terms and notional principal. Lastly, financial intermediaries can act as market makers. When counterparties for a specific swap agreement over a specific notional principal are not available, financial intermediaries can step in and act as the counterparty to this agreement. This process is known as market making. Therefore, all three roles - I, II, and III - are correctly attributed to financial intermediaries in swap agreements.

Choice A is incorrect. While Role I is correctly attributed to financial intermediaries, as they ensure the obligation of swap agreements is honored even in the event of a default by one party, Role II is not exclusive to them. Financial intermediaries do have the ability to enter into two offsetting transactions in a swap agreement without the knowledge of both parties involved, but this role can also be performed by other entities in financial markets.