Which of the following contributed to the collapse of command economies in communist countries around the end of the cold war?

a. countries with command economies allowed wealthy factory owners to exploit their lower-class workers.

b. countries with command economies failed to produce enough consumer goods, including food, for their citizens.

c. countries with command economies created problems, such as high unemployment, by reducing government spending.

d. countries with command economies prevented the government from regulating employee safety and pollution.