"when the economist says that material wants are insatiable, he means that: " a. the structure of consumer wants is highly unpredictable. b. the structure of consumer demand varies from time to time and from country to country. c. these wants are virtually unlimited and therefore incapable of complete satisfaction. d. economic resources -- land, labor, capital, and entrepreneurial ability -- are scarce. e. economic resources are valuable only because they can be used to produce consumer goods.