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 spinning class has risen from $20 to $30, then

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