Questions 14 to 16 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now, listen to the passage. The Mafia went out of the liquor business, because ______

A．the quality of regulated liquor became assured and taxed
B．the bootlegging became a source of public revenue
C．they settled trade disputes with gunfire but without profit
D．there was no more revenue worth risking their lives