What is an example of commodity money?

a. coins

b. precious stones

c. a tractor

d. currency

I would say b. precious stones Example of commodities that have been used as mediums of exchange include gold, silver, copper, salt, peppercorns, tea, large stones (such as Rai stones), decorated belts, shells, alcohol, cigarettes, cannabis, candy, cocoa beans, cowries and barley.