If the Price of Pizzas Has Risen from $4 to $5

Multiple Choice

If the price of pizzas has risen from $4 to $5 at the same time that the price of an hour of aerobics class has risen from $20 to $30, then

A) pizzas have become relatively more expensive.
B) aerobics classes have become relatively more expensive.
C) the relative prices of pizzas and aerobics classes have remained constant.
D) workers' real income must have decreased.