18. Shortages and black markets largely came to an end in the Soviet Union because a. Ronald Reagan showed that the ideas of Jean Baptiste Say and Adam Smith were more efficient economic models than the ideas put forth by Karl Marx. b. Barack Obama sped up the rate at which the Soviet Union collapsed by making shortages there worse in the short run. c. Franklin Roosevelt worked with Hugo Chavez to implement price controls on the Soviet economy, leading to the economic collapse occurring today. d. Ronald Reagan modeled his economic policies on what Karl Marx advocated to determine how food would be supplied. e. Donald Trump imposed tariffs on the Soviet economy