[单选题]8.Which of the following is not true for a nation that is in equilibrium in isolation? A.A.It consumes inside its production frontier B.B.it reaches the highest indifference curve possible with its production frontier C.C.the indifference curve is tangent to the nation's production frontier D.D.MRT of X for Y equals MRS of X for Y, and they are equal to Px/Py