Excluding purchases by businesses, the average amount spent on a factory-new car has risen 30 percent in the last five years. In the average household budget, the proportion spent on car purchases has remained unchanged in that period. Therefore the average household budget must have increased by 30 percent over the last five years.

Which of the following is an assumption on which the argument relies？

(A)The average number of factory-new cars purchased per household has remained unchanged over the last five years.
(B)The average amount spent per car by businesses buying factory-new cars has risen 30 percent in the last five years.
(C)The proportion of the average household budget spent on all car-related expenses has remained unchanged over the last five years.
(D)The proportion of the average household budget spent on food and housing has remained unchanged over the last five years.
(E)The total amount spent nationwide on factory- new cars has increased by 30 percent over the last five years.