If the consumer wants to buy $$x_1$$ units of item 1 and $$x_2$$ units of item 2 and the prices of the two items are $$p_1$$ and $$p_2$$ respectively, and M is the income of the consumer, then $$ p_1 x_1 + p_2 x_2 \leq M$$ is called the consumer's _______ .

A

demand graph

B

utility function

C

budget constraint

D

indifference curve