For a currency to function effectively as a medium of exchange, it must be widely accepted by people involved in transactions. The most relevant characteristic from your options would be:
- if it is accepted with a known currency, like the dollar
This indicates that the currency can be exchanged for goods and services, thus fulfilling the role of a medium of exchange. While the other characteristics mentioned may contribute to the overall effectiveness or stability of the currency, acceptance is key to its function as a medium of exchange.