A Production Possibilities Frontier Is a Straight Line When

A production possibilities frontier is a straight line when

A) the more resources the economy uses to produce one good,the fewer resources it has available to produce the other good.
B) an economy is interdependent and engaged in trade instead of self-sufficient.
C) the rate of tradeoff between the two goods being produced is constant.
D) the rate of tradeoff between the two goods being produced depends on how much of each good is being produced.