Farmer Fred is paid by the government to leave a fourth of his cropland unplanted during the next growing season. Farmer Fred's vegetables will probably be more expensive because of the reduced supply, so the government decides to give each villager in Fred's town a set of vouchers that can only be spent at Fred's farm. Farmer Fred can turn in the vouchers to the government later in exchange for cash. Which of the following agricultural policies has the government employed? 

a. Price supports 

b. Supply restrictions 

c. Demand enhancement 

d. Income support 

e. Both a and b

f. Both b and c