Which of the Following Is Often Referred to as the Basic

Which of the following is often referred to as the basic postulate of economics?

A) Individuals act only out of selfish motives.
B) Incentives matter--individuals respond in predictable ways to changes in personal costs and benefits.
C) The accuracy of the assumptions is the best test of an economic theory.
D) The value of a good is objective; it is equal to the cost of producing the good.