Suppose one observes that when the price of peanut butter increases, the demand for jelly increases. One must conclude that:

Suppose one observes that when the price of peanut butter increases, the demand for jelly increases. One must conclude that:
A.peanut butter and jelly are complements.
B.peanut butter and jelly are inferior goods.
C.peanut butter and jelly are normal goods.
D.peanut butter and jelly are substitutes.
正确答案：peanut butter and jelly are substitutes.