问题
单项选择题
In Paragraph 5, "two-tier system" means some ______.
A．men have many wives while others have none
B．people are very rich while others are very poor
C．people have too much work to do while others have nothing to do
D．people control others
答案
参考答案：B
解析：[分析] 细节题型。 参看第五段的第一句话The economy of North America has resulted in...。