Individual indifference curves differ from person to person

a. therefore, they must be averaged to determine a community indifference curve for an individual product

b. and, therefore, they are not considered in determining benefits of international trade.

c. so, there is no completely accurate way to combine individual indifference curves to arrive at a community indifference curve.

d. but they can still be combined to determine a community indifference curve if a large enough sample is used