Which of the following is a true statement?

a. Unanticipated inflation is a change in the general level of prices that catches most decision makers by surprise.
b. High and variable rates of inflation are easy for decision makers to forecast accurately.
c. High and variable rates of inflation can increase GDP by reducing investment.
d. When decision-makers are able to anticipate slow, steady rates of inflation, prices become more unstable and there is a negative impact on the level of prosperity.

A