NO.PZ2016010801000016
问题如下：
When there is a decrease in the price of good X, and the consumption of good X also decreases, which of the following statements about the substitution effect and the income effect is most accurate?
选项：
A.Both the substitution effect and the income effect are positive.
B.Both the substitution effect and the income effect are negative.
C.The substitution effect is positive and the income effect is negative.
解释：
C is correct.
If X’s price is decreasing, the substitution effect will lead a consumer to consume more of X and consume less substitution of X, which remains the previous price. The substitution effect is positive. In this question, consumption of X is decreasing as well, therefore, income effect has to be negative and larger than substitution effect.
考点：替代效应和收入效应。
解析：无论什么商品，它的替代效应总是正的，所以A选项不正确。
但是X的价格下降后，需求量出现下降，可见，其收入效应表现为负效应，所以B选项错误。C选项正确。
为什么替代效应总是正的？
