51. In line 8, paragraph 1, "the desire of individuals to maximize their incomes" means ________.
[A] Americans are never satisfied with their incomes
[b)Americans tend to overstate their incomes
[C] Americans want to have their incomes increased
[D] Americans want to increase the purchasing power of their incomes
52. The first two sentences in the second paragraph tell us that ________.
[A] producers can satisfy the consumers by mechanized production
[b) consumers can express their demands through producers
[C] producers decide the prices of products
[D] supply and demand regulate prices
53. According to the passage, a private-enterprise economy is characterized by ________.
[A] private property and rights concerned
[b) manpower and natural resources control
[C] ownership of productive resources
[D] free contracts and prices
54. The passage is mainly about ________.
[A] how American goods are produced
[b) how American consumers buy their goods
[C] how American economic system works
[D] how American businessmen make their profits