NO.PZ2016121201000002
问题如下：
When income elasticity is negative, the good should be classified as
选项：
A.an inferior good.
B.an normal good.
C.luxuries.
解释：
A is correct.
The income elasticity of an inferior good is negative.
弹性不是都是负的麻，我选了normal good，这题考点和答案分别是什么意思呢，谢谢老师
