A black market is
a. Very similar to a​ "gray" market except that the goods and services exchanged are imported.
b. A market in which buying and selling take place at prices consistent with government price regulations.
c. A market in which all transactions involve activities​ (such illicit​ drugs, prostitution,​ etc.) many in the population find morally offensive.
d. A market in which buying and selling take place at prices that violate government price regulations.