During the 1990 's the black - market price of heroin decreased from $230 per gram to $75 per gram. At the smae time, the quantity of heroin consumed increased by about 100 metric tons. This outcome is most consistent with:
A. An increase in the supply of heroin
B. A decrease in the demand for heroin
C. A decrease in both the supply and demand for heroin
D. A decrease in the supply of heroin