Suppose that if the price of plane tickets increased, more people would choose to travel by train. If this happened, you would know that:

Suppose that if the price of plane tickets increased, more people would choose to travel by train. If this happened, you would know that:
A.plane tickets are an inferior good.
B.the cross-price elasticity between plane tickets and train tickets is positive.
C.plane tickets and train tickets are complements.
D.the cross-price elasticity between plane tickets and train tickets is negative.
正确答案：the cross-price elasticity between plane tickets and train tickets is positive.