The price of gasoline is $2.50 per gallon at the closest gas station, but is only $2.30 per gallon at a gas station two miles away. By driving to the farther gas station, opportunity cost is:

a) non-existent because gas is cheaper at the farther station.

b) $0.20 per gallon, the difference in price between the two gas stations.

c) the cost of filling one’s tank at the original price of $2.50 per gallon.

d) the value of one’s time and expenses to go to the farther gas station.