单项选择题

According to the passage, it has long been believed that ______.

A.people in poor countries scarcely know how to enjoy a high standard of living
B.the world's resources being limited, the people in underdeveloped countries are bound to live a poor life
C.most Americans know that the world's resources of many kinds are becoming scarce
D.it is impossible for all the people in the world to improve their living standards