Which of the following exchange rate regimes are considered hard pegs?
a. Setting the exchange rate by legislation and then backing holding 100% reserves of foreign currency to back the amount of national currency in circulation.
b. Controlling the domestic interest rate as needed to keep the exchange rate at or near a central value.
c. Abandoning use of a national currency to use the currency of another country.
d. Buying or selling reserves of foreign currency as needed to keep the exchange rate at or near a central value.