What Is a National Paper Currency Standard

What is a national paper currency standard?

A) Governments issue a currency and peg its value to gold.
B) Governments issue a currency and commit to exchanging the currency for a set gold price.
C) Governments issue a currency and use gold as a standard value but do not commit to exchanging gold for the currency.
D) Governments issue a currency and commit to supporting the value of the currency.
E) Governments issue a currency but make no efforts to support the currency.