In which type of economy do the forces of supply and demand typically drive prices?

a. a market economy

b. a traditional economy

c. a planned economy

d. a command economy

The kind of economy that is determined by supply and demand is a market economy - answer a) is the correct one

In a command and planned economies the government decides over prizes and production (the two are roughly synonymous).

A traditional economy is an economy based on exchange, not money.