You need to build a model that predicts the volume of sales (Y) as a function of advertising (X). You believe that sales increase as advertising increase, but at a decreasing rate. Which of the following would be the general form of such model? (note: X^2 means X Square)

	A.	Y ^ = b0 + b1 X1 + b2 X2^2
	B.	Y ^ = b0 + b1 X + b2 X / X^2
	C.	Y ^ = b0 + b1 X + b2 X^2
	D.	Y ^ = b0 + b1 X
	E.	Y ^ = b0 + b1 X1 + b2 X2