单项选择题
玉米的起源地是（）。
A．中国 B．印度 C．地中海 D．墨西哥
单项选择题 Adam Smith saw that the division of labor
单项选择题 According to the writer, Adam Smith's mistake was in believing that the division of labor______.
单项选择题 According to the writer, which one of the following is NOT true
