For two goods X and Y to be classified as substitutes, it must be the case that:

For two goods X and Y to be classified as substitutes, it must be the case that:
A.when the price of X rises, the demand for Y decreases.
B.X and Y are identical.
C.consumers tend to purchase both items.
D.when the price of X rises, the demand for Y increases.
正确答案：when the price of X rises, the demand for Y increases.