A Consumer's Demand for Tuna Can Be Found from an Indifference

A consumer's demand for tuna can be found from an indifference curve diagram by doing which of the following?

A) observing what happens to the consumption of tuna for different income levels
B) finding where the budget line is tangent to an indifference curve for one price of tuna
C) allowing the price of tuna to change and observing the different best, affordable levels of tuna
D) changing the indifference curves and seeing the changes in the quantity of tuna the consumer demands
E) it is impossible to derive a demand curve from an indifference curve graph